Example 2:
We can find 50% of a value by multiplying 1 2 with the value. Will multiplying the value by 0.5 also give the answer for 50% of the value?
Yes, since 1/2 = 0.5
50% = 50 /100 = 1/2 = 0.5
50% of 24 = 12
0.5 x 24 = 12
Complete the following table
Example 3:
The maximum marks in a test are 75. If students score 80%
or above in the test, they get an A grade. How much should Zubin score
at least to get an A grade?
Example 4:
To prepare a particular millet kanji (porridge), suppose the
ratio of millet to water to be mixed for boiling is 2:7. What percentage
does the millet constitute in this mixture? If 500 ml of the mixture is to
be made, how much millet should be used?
The ratio of millet to the volume of the
mixture is 2:9.
In other words, in one unit
of the mixture, millet occupies 2 /9 units and
water occupies 7/ 9 units.
The percentage (i.e., in 100 such units) of
millet in the mixture is 2/9 x 100 = 22.22%.
The percentage of water in the mixture will
be 100 – 22.22 = 77.78%.
A mixture with 22.22% millet means
100 ml mixture will have 22.22 ml millet.
Therefore, 500 ml with 22.22% millet will have 5 × 22.22 = 111.1 ml of
millet.
Example 5:
A cyclist cycles from Delhi to Agra and completes 40% of the
journey. If he has covered 92 km, how many more kilometres does he
have to travel to reach Agra?
Kishanlal recently opened a garment shop. He aims to
achieve a daily sales of at least ₹5000. The sales on the first 2 days were
₹2000 and ₹3500. What percentage of his target did he achieve?
It is 40% on Day 1 and 70% on Day 2.
Another way of saying it is — he was 60% short of his target on Day 1
and 30% short of his target on Day 2.
In the next two days, he made ₹5000 and ₹6000 respectively. What
percentage of his target are these values?What percentage of the target was achieved on Day 4?
His target is ₹5000, and he made ₹5000 on Day 3 — this is 100%.
On
Day 4, he made ₹6000, which is 1000 more than his target.
1000 is 20% of 5000. Therefore, 6000, (5000 + 1000) is 100% + 20%
= 120% of 5000. It can also be computed as 6000 / 5000 × 100 = 6 / 5 × 100 = 120%.
This means he achieved 120% of his target, i.e., 20% more than his target.
On Days 5 and 6 his sales were ₹7800 and ₹9550 respectively. Calculate
the percentage of the target achieved on these days.
On Day 7, he achieved 150% of his target. On Day 8, he achieved 210% of
his target. Find the sales made on these days.
Suppose on some day, he made ₹2500. This can be expressed as “He
achieved 1
2 of his target” or “He achieved 50% of his target” or “He
achieved 0.5 of his target”. On some other day, he made ₹10,000. We
can say “He achieved twice/double/2 times his target” or “He achieved
200% of his target”
Complete the table below. Mark the approximate locations in the
following diagram.
Example 7:
A farmer harvested 260 kg of wheat last year. This year, they
harvested 650 kg of wheat. What percentage of last year’s harvest is this
year’s harvest?
This year’s harvest = \( \frac{650}{260} \) × 100 = 250% of last year’s harvest.
250% indicates that it is 2.5 times the original value
Figure it Out Page 12
Estimate first before making any computations to solve the following
questions. Try different methods including mental computations.
1. Find the missing numbers. The first problem has been worked out
(i) The whole bar = 100%
It is divided into 5 equal parts
One part = 20%
Next bar : - The full bar (100%) = 75
Bar divided into 5 equal parts
100%
┌───┬───┬───┬───┬───┐
│20% │20% │20% │20%│20% │
└───┴───┴───┴───┴───┘
Value of 1 part= 75/5= 15 The arrow shows the four bars
Missing value = 15 x 4 = 60
(ii) The bar is divided into 10 equal parts
Whole bar = 100%
Each part= (100%)/10=10%
100%
┌─┬─┬─┬─┬─┬─┬─┬─┬─┬─┐
│ │ │ │ │ │ │ │ │ │ │
└─┴─┴─┴─┴─┴─┴─┴─┴─┴─┘
Each part = 10%
Missing value = 10%
Next bar : - The full bar (100%) = 90
Bar divided into 10 equal parts
90
┌─┬─┬─┬─┬─┬─┬─┬─┬─┬─┐
│9 │9 │9│9 │9 │9 │9 │9 │9│9 │
└─┴─┴─┴─┴─┴─┴─┴─┴─┴─┘
Value of 1 part= 90/10= 9 The arrow shows the six parts
Missing value = 9 x 6 = 54
(iii) Left diagram
Bar divided into 4 equal parts
Whole = 100%
100%
┌────┬────┬────┬────┐
│25% │25% │25% │25% │
└────┴────┴────┴────┘
Each part= (100%)/4 = 25% Arrow indicates one part
Missing value = 25%
Right diagram
Whole bar (100%) = 140
Divided into 4 equal parts
140
┌────┬────┬────┬────┐
│35 │35 │35 │35 │
└────┴────┴────┴────┘
Each part= (140 %)/4 =35 Arrow shows the three parts
Missing value = 3 x 35 = 105
2. Find the value of the following and also draw their bar models.
(i) 25% of 160
(ii) 16% of 250
(iv) 140% of 40
(v) 1% of 1 hour
(iii) 62% of 360
(vi) 7% of 10 kg
(i) 25% of 160
160
┌────┬────┬────┬────┐
│40 │40 │40 │40
└────┴────┴────┴────┘
25% = 40
250
┌──── ┬──────────────┐
│ 16% | 84% │
│ 40 | │
└─────┴──────────────┘
(iii) 62% of 360
360
┌───────────────┬────────┐
│ 62% │ 38% │
│ 223.2 │ │
└───────────────┴────────┘
(iv) 140% of 40
40 + 40 + 20
┌────┬────┬────┐
│40 │40 │20 │
└────┴────┴────┘
140% = 56
(v) 1% of 1 hour
60 minutes
┌──────────────────────────────┐
│1% | |
= 0.6 |min │
│ | |
= 36 | sec │
└──────────────────────────────┘
(vi) 7% of 10 kg
10 kg
┌──────────────────────────────┐
│ 7% | |
= 0.7 kg | │
│ | |
= 700 g | │
└──────────────────────────────┘
3. Surya made 60 ml of deep orange paint, how much red paint did he
use if red paint made up 3
4 of the deep orange paint?
Calculation:
Answer:
Surya used 45 ml of red paint.
4. Pairs of quantities are shown below. Identify and write appropriate
symbols ‘>’, ‘<’, ‘=’ in the boxes. Visualising or estimating can help.
Compute only if necessary or for verification.
(i) 50% of 510 ______ 50% of 515
(ii) 37% of 148 ______73% of 148
(iii) 29% of 43 ______ 92% of 110
(iv) 30% of 40 ______40% of 50
(v) 45% of 200 ______10% of 490
(vi) 30% of 80 ______24% of 64
(i) 50% of 510 ⬜ 50% of 515
-
50% of 510 = 255
-
50% of 515 = 257.5
Answer:
(ii) 37% of 148 ⬜ 73% of 148
Same number, but 73% > 37%
Answer:
(iii) 29% of 43 ⬜ 92% of 110
-
29% of 43 ≈ 12.47
-
92% of 110 = 101.2
12.47<101.2
Answer:
(iv) 30% of 40 ⬜ 40% of 50
-
30% of 40 = 12
-
40% of 50 = 20
12<20
Answer:
(v) 45% of 200 ⬜ 10% of 490
-
45% of 200 = 90
-
10% of 490 = 49
Answer:
(vi) 30% of 80 ⬜ 24% of 64
-
30% of 80 = 24
-
24% of 64 = 15.36
Answer:
5. Fill in the blanks appropriately:
(i) 30% of k is 70, 60% of k is _____, 90% of k is _____, 120% of k
is ______.
(ii) 100% of m is 215, 10% of m is _____, 1% of m is ______, 6% of m
is ______.
(iii) 90% of n is 270, 9% of n is ______, 18% of n is _____, 100% of n
is ______.
(iv) Make 2 more such questions and challenge your peers.
(i) 30% of k = 70
Now,
60% of k = 90% of k = 120% of k =
Answers:
60% = 140, 90% = 210, 120% = 280
(ii)
100% of m = 215
-
10% of m =
-
1% of m =
-
6% of m =
Answers:
10% = 21.5, 1% = 2.15, 6% = 12.9
(iii)
90% of n = 270
9% of n = 9×3=27
18% of n = 18×3=54
100% of n = 100×3=300
Answers:
9% = 27, 18% = 54, 100% = 300
(iv) Two sample questions
-
If 25% of a number is 50, find 100% of the number.
-
If 40% of a number is 120, find 10% and 80% of the number.
6. Fill in the blanks:
(i) 3 is ____ % of 300.
(ii) _____ is 40% of 4.
(iii) 40 is 80% of _____.
(i) 3 is ___% of 300
Answer: 1%
(ii) ___ is 40% of 4
Answer: 1.6
(iii) 40 is 80% of ___
Answer: 50
7. Is 10% of a day longer than 1% of a week? Create such questions
and challenge your peers.
Is 10% of a day longer than 1% of a week?
Since, 2.4>1.68
Yes, 10% of a day is longer than 1% of a week.
Create a similar challenge question
Example:
Is 5% of a year longer than 10% of a month?
(Students can compare by converting into days)
8. Mariam’s farm has a peculiar bull. One day she gave the bull
2 units of fodder and the bull ate 1 unit. The next day, she gave
the bull 3 units of fodder and the bull ate 2 units. The day after,
she gave the bull 4 units and the bull ate 3 units. This continued,
and on the 99th day she gave the bull 100 units and the bull ate
99 units. Represent these quantities as percentages. This task
can be distributed among the class. What do you observe?
Mariam gave the bull:
-
Day 1: 2 units → ate 1 → ate
-
Day 2: 3 units → ate 2 → ate
-
Day 3: 4 units → ate 3 → ate
-
…
-
Day 99: 100 units → ate 99 → ate
Observation:
As days increase,
So the bull eats a larger percentage each day as the total given increases.
9. Workers in a coffee plantation take 18 days to pick coffee berries in
20% of the plantation. How many days will they take to complete
the picking work for the entire plantation, assuming the rate of
work stays the same? Why is this assumption necessary?
Workers take 18 days to finish 20% of the plantation.
If 20% takes 18 days, then full (100%) takes:
Answer: 90 days
10. The badminton coach has planned the training
sessions such that the ratio of warm up : play : cool
down is 10% : 80% : 10%. If he wants to conduct a
training of 90 minutes. How long should each activity
be done?
Total training = 90 minutes, ratio:
-
Warm-up = 10%
-
Play = 80%
-
Cool-down = 10%
Time allocated:
-
Warm-up = 9 min
-
Play = 72 min
-
Cool-down = 9 min
11. An estimated 90% of the world’s population lives in the Northern
Hemisphere. Find the (approximate) number of people living in the
Northern Hemisphere based on this year’s worldwide population.
Current estimated world population (as of January 1, 2026) is approximately 8,266,435,578 people.
If about 90% of the world’s population lives in the Northern Hemisphere, then:
Approximate number of people in the Northern Hemisphere: ~7.44 billion.
12. A recipe for the dish, halwa, for 4 people has the following
ingredients in the given proportions — Rava: 40%, Sugar: 40%, and
Ghee: 20%.
(i) If you want to make halwa for 8 people, what is the proportion
of each of the above ingredients?
(ii) If the total weight of the ingredients is 2 kg, how much rava,
sugar and ghee are present?
Given proportions:
Rava = 40%
Sugar = 40%
Ghee = 20%
(i) For 8 people
8 is double 4, so ingredients double too:
Rava = 40% of total doubled → stays 40%
Sugar = 40%
Ghee = 20%
Proportions remain the same: 40%, 40%, 20%
(ii) If total = 2 kgConvert % to weight:Rava =40% of 2=0.40×2=0.8 kgSugar =40% of 2=0.8 kg
Ghee =20% of 2=0.4 kgIngredient weights:Rava = 0.8 kgSugar = 0.8 kgGhee = 0.4 kg
Example 1:
Eesha scored 42 marks out of 50 on an English test and 70
marks out of 80 in a Science test. Since she lost only 8 marks in English
but 10 marks in Science, she thinks she has done better at English. Reema
does not agree! She argues that since Eesha has scored more marks in
Science, she has done better at Science. Vishu thinks we cannot compare
the scores because the maximum marks are different. Who do you think
is correct?
If the maximum marks are the same, the comparison becomes easier,
isn’t it?
English score as a percentage = \( \frac{42}{50} \) × 100 = 84%
Science score as a percentage = \( \frac{70}{80} \) × 100 = 87.5%.
The Science score (as a percentage) is higher than the English score
(as a percentage).
So, Eesha has scored better on
the Science test
Example 2: Madhu and
Madhav recently learnt about
the importance of reading
labels on processed food
before purchase. They are at
a shop to buy badam drink
mix. They are looking at two
products
and
wondering
which has a larger share of
badam. Can you figure it out?
Which product uses a smaller
proportion of food chemicals?
DEF’s sugar content as a percentage of total weight = 99
150 × 100 = 66%Product 1: DEF Badam Mix
Total weight = 150 g
| Ingredient | Weight (g) |
|---|
| Sugar | 99 g |
| Milk solids | 30 g |
| Badam powder | 12 g |
| Food chemicals | 9 g
|
Product 2: Zacni Badam Mix
Total weight = 400 g
| Ingredient | Weight (g) |
|---|
| Sugar | 227 g |
| Milk solids | 64 g |
| Badam powder | 40 g |
| Food chemicals | 24 g
|
Percentage= \( \frac{Part}{Total} \) ×100
DEF Badam Mix (Total = 150 g)
Zacni Badam Mix (Total = 400 g)
Check:
| Product | Sugar | Milk Solids | Badam Powder | Food Chemicals |
|---|
| DEF | 66% | 20% | 8% | 6% |
| Zacni | 56.75% | 16% | 10% | 6% |
Which product has a larger share of badam?
Zacni has a larger share of badam powder.
Which product uses a smaller proportion of food chemicals?
Both products use the same proportion of food chemicals (6%).
Percentages help us compare products fairly, even when packet sizes are different.
Reading labels carefully helps us make healthier choices.
Example 3:
Do the following two statements mean the same thing?
(i) The population of this state in 1991 is 165% of that in 1961.
(ii) The population of this state has increased by 65% from 1961 to 1991.
Yes, both mean the same. Suppose p is the population of the state in
1961 and q is the population of the state in 1991.
Statement A implies,
q = 165% of p,
\( \frac{165}{100} \) p = 1.65p
Statement B implies,
q = p + 65% of p
q = p + 0.65 × p = 1.65p
The population of the state in 1991 is 1.65 times that
in 1961
Figure it Out Page - 19
1. If a shopkeeper buys a geometry box for ₹75 and sells it for ₹110,
what is his profit margin with respect to the cost?
Cost Price (CP) = ₹75
Selling Price (SP) = ₹110
Profit = SP − CP = 110 − 75 = ₹35
Profit % = \( \frac{35}{75} \) x 100 = 46
\( \frac{2}{3} \)%
2. I am a carpenter and I make chairs. The cost of materials for a chair
is ₹475 and I want to have a profit margin of 50%. At what price
should I sell a chair?
Cost of materials = ₹475
Profit margin required = 50%
Selling Price = 475 + 237.5 = ₹712.50
Answer: He should sell the chair for ₹712.50
3. The total sales of a company (also called revenue) was ₹2.5 crore
last year. They had a healthy profit margin of 25%. What was the
total expenditure (costs) of the company last year?
Revenue (Sales) = ₹2.5 crore
Profit margin = 25%
Profit = 25% of expenditure
So, Revenue = Cost + Profit = 125% of cost
Answer: Total expenditure = ₹2 crore
4. A clothing shop offers a 25% discount on all shirts. If the original
price of a shirt is ₹300, how much will Anwar have to pay to buy
this shirt?
Marked Price = ₹300
Discount = 25%
Amount to pay = 300 − 75 = ₹225
Answer: Anwar pays ₹225
5. The petrol price in 2015 was ₹60 and ₹100 in 2025. What is the
percentage increase in the price of petrol?
(i) 50%
(ii) 40%
(iv) 66.66%
(v) 140%
(iii) 60%
(vi) 160.66%
Old price = ₹60
New price = ₹100
Increase = 100 − 60 = 40
Correct option: (iv) 66.66%
3. Samson bought a car for ₹4,40,000 after getting a 15% discount from
the car dealer. What was the original price of the car?
Discount = 15%
So, SP = 85% of original price
Answer: Original price ≈ ₹5,17,650 (approx.)
4. 1600 people voted in an election and the winner got 500 votes. What
percent of the total votes did the winner get? Can you guess the
minimum number of candidates who stood for the election?
Total votes = 1600
Votes for winner = 500
Minimum number of candidates?
Remaining votes = 1100
If there were only 2 candidates, the other would get 1100 votes → winner impossible.
So, minimum = 3 candidates
Answer:
-
Winner got 31.25% votes
-
Minimum candidates = 3
5. The price of 1 kg of rice was ₹38 in 2024. It is ₹42 in 2025. What is the
rate of inflation? (Inflation is the percentage increase in prices.)
Old price = ₹38
New price = ₹42
Increase = 4
Answer: Inflation ≈ 10.5%
6. A number increased by 20% becomes 90. What is the number?
A number increased by 20% becomes 90
Answer: The number is 75
7. A milkman sold two buffaloes for ₹80,000 each. On one of them, he
made a profit of 5% and on the other a loss of 10%. Find his overall
profit or loss.
SP of each buffalo = ₹80,000
First buffalo (5% profit)
Second buffalo (10% loss)
Total CP ≈ 1,65,079
Total SP = 1,60,000
Loss = 5,079
Loss % = \( \frac{5079}{165079} \) x 100 approx 3.08%
Answer: Overall loss of about 3%
8. The population of elephants in a national park increased by 5% in
the last decade. If the population of the elephants last decade is p,
the population now is
(i)
p × 0.5
(iv) p × 1.05
(ii)
(v)
p × 0.05
p + 1.50
(iii)
p × 1.5
Population last decade = p
Increase = 5%
Correct option: (iv) p × 1.05
9. Which of the following statement(s) mean the same as — “The
demand for cameras has fallen by 85% in the last decade”?
(i) The demand now is 85% of the demand a decade ago.
(ii)
The demand a decade ago was 85% of the demand now.
(iii)
The demand now is 15% of the demand a decade ago.
(iv) The demand a decade ago was 15% of the demand now.
(v) The demand a decade ago was 185% of the demand now.
(vi) The demand now is 185% of the demand a decade ago.
If demand fell by 85%, only 15% remains.
Correct statements:
(iii) Demand now is 15% of the demand a decade ago
(iv) Demand a decade ago was 15% of the demand now (wrong logic)
Correct meanings:
Answer: Only (iii)
Example 7:
If one deposits ₹6000 in the bank, what is the amount after
3 years?
That depends on the choice of FD. There are two possibilities:
1. Option 1: The interest is paid out regularly (for example, every year).
The principal amount is returned after the maturity period
2. Option 2: The interest gained every time (say after each year) is
added back to the FD, thus increasing the principal amount for the
subsequent period. After the maturity period, the entire amount is
returned. This phenomenon is called compounding.
Example 8:
What percent is the total amount received with respect to
the amount deposited in both the options?
This can be calculated by finding total amount received
amount deposited × 100.
Without Compounding
7800 /6000 × 100 = 130% = 1.3.
The total amount
received = 6000 × (1 + 0.1 + 0.1 + 0.1)
= 6000 × 1.3.
The percentage gain over 3 years is 30%.
With Compounding
7986 /6000 × 100 = 133.1% = 1.331.
The total amount received
= 6000 × 1.1 × 1.1 × 1.1.
= 6000 × 1.331
The percentage gain over 3 years is 33.1%
Figure it Out page no 22-23
1. Bank of Yahapur offers an interest of 10% p.a. Compare how
much one gets if they deposit ₹20,000 for a period of 2 years with
compounding and without compounding annually.
1. Bank of Yahapur (10% p.a., 2 years, ₹20,000)
(A) Without compounding (Simple Interest)
Formula:
Amount received = 20,000 + 4,000 = ₹24,000
(B) With compounding annually
Year 1:
Year 2:
Final amount = 22,000 + 2,200 = ₹24,200
| Method | Amount |
|---|
| Without compounding | ₹24,000 |
| With compounding | ₹24,200 |
₹200 more with compounding
2. Bank of Wahapur offers an interest of 5% p.a. Compare how
much one gets if one deposits ₹20,000 for a period of 4 years with
compounding and without compounding annually.
2. Bank of Wahapur (5% p.a., 4 years, ₹20,000)
(A) Without compounding
Amount = 20,000 + 4,000 = ₹24,000
(B) With compounding annually
Year-wise:
| Year | Amount (₹) |
|---|
| Start | 20,000 |
| After 1 year | 21,000 |
| After 2 years | 22,050 |
| After 3 years | 23,152.50 |
| After 4 years | 24,310.13 |
| Method | Amount |
|---|
| Without compounding | ₹24,000 |
| With compounding | ₹24,310.13
|
3. Do you observe anything interesting in the solutions of the two
questions above? Share and discuss.
Let us try to generalise the pattern observed in each of the options.
Observations
Compounding always gives more amount than simple interest.
Difference increases with time.
Interest is earned on interest itself in compounding.
Generalisation
If
Principal =
Rate =
Time = years
Without compounding (Simple Interest):
With compounding (annually):
Example 9:
What is the amount we get back if we invest ₹6000 at an
interest rate of 10% p.a. for ‘t’ years?
Then, find the formula for total interest gained for both:
-
(a) Without compounding (Simple Interest)
-
(b) With compounding (Compound Interest, annually)
(A) Without Compounding (Simple Interest)
Given:
Principal
Rate Time years
Amount after years:
Total Interest gained:
Observation:
Interest increases by a fixed amount every year → linear growth
(B) With Compounding (Compound Interest – Annually)
Amount after years:
Total Interest gained:
π Observation:
Interest is earned on interest + principal → exponential growth
Suppose we want to know the expression/formula to find the total
interest amount gained at the end of the maturity period. What
would be the formula for each of the two options?
Generalised Formula
| Type of Interest | Amount Formula | Interest Formula |
|---|
| Simple Interest | ( A = P(1 + rt) ) | ( I = Prt ) |
| Compound Interest | ( A = P(1 + r)^t ) | ( I = P[(1+r)^t - 1] ) |
Key Continuity Idea
Without compounding: growth is linear
-
With compounding: growth is exponential
-
For small , both are close
-
As increases, compound interest becomes much larger
This links directly to population growth, bacteria growth, inflation, etc.
Figure it Out page 23
4. Jasmine invests amount ‘p’ for 4 years at an interest of 6% p.a. Which
of the following expression(s) describe the total amount she will get
after 4 years when compounding is not done?
(i) p × 6 × 4
(ii) p × 0.6 × 4
(iii) p × 0.6 /100 × 4
(iv) p × 0.06 /100 × 4
(v) p × 1.6 × 4
(vi) p × 1.06 × 4
(vii) p + (p × 0.06 × 4)
4. Jasmine invests ₹p for 4 years at 6% (No compounding)
Correct expression:
Correct option:
(vii)
5. The post office offers an interest of 7% p.a. How much interest would
one get if one invests ₹50,000 for 3 years without compounding?
How much more would one get if it was compounded?
Without compounding
With compounding
Interest = 61,250 − 50,000 = ₹11,250
| Method | Interest |
|---|
| Without compounding | ₹10,500 |
| With compounding | ₹11,250
|
₹750 more with compounding
6. Giridhar borrows a loan of ₹12,500 at 12% per annum for 3 years
without compounding and Raghava borrows the same amount for
the same time period at 10% per annum, compounded annually.
Who pays more interest and by how much?
Giridhar
Raghava
Interest = 16,637.5 − 12,500 = ₹4,137.50
Conclusion
-
Giridhar pays ₹4,500
-
Raghava pays ₹4,137.50
Giridhar pays ₹362.50 more
7. Consider an amount ₹1000. If this grows at 10% p.a., how long
will it take to double when compounding is done vs. when
compounding is not done? Is compounding an example of
exponential growth and not-compounding an example of linear
growth?
Without compounding
With compounding
Conclusion
8. The population of a city is rising by about 3% every year. If the
current population is 1.5 crore, what is the expected population
after 3 years?
Expected population ≈ 1.64 crore
9. In a laboratory, the number of bacteria in a certain experiment
increases at the rate of 2.5% per hour. Find the number of bacteria
at the end of 2 hours if the initial count is 5,06,000.
Initial = 5,06,000
Rate = 2.5% per hour
Time = 2 hours
Final bacteria ≈ 5,31,616
Example 10:
A TV is bought at a price of ₹21,000. After 1 year, the value
of the TV depreciates by 5%. Find the value of the TV after one year.
The amount of reduction in the
value is 5% of 21,000 = 0.05 × 21,000
= 1050.
The current value is 21,000 – 1050
= 19,950.
The value of the TV after 1 year will
be 95% of the current value
= 95% of 21,000 = 0.95 × 21,000
= 19,950.
The value of the TV after 1 year will be ₹19,950.
Example 11:
The population of a village was observed to be reducing by
about 10% every decade. If the current population is 1250, what is the
expected population after 3 decades?
The population 1 decade later will
be 0.9 times the population of the
current decade.
Therefore, the population after
1 decade will be 1250 × 0.9.
The population after 2 decades will
be 1250 × 0.9 × 0.9.
The population after 3 decades will
be 1250 × 0.9 × 0.9 × 0.9
= 911.25
First decade’s decrease = 0.1 × 1250
= 125.
Population after 1 decade
= 1250 – 125 = 1125.
Second decade’s decrease
= 0.1 × 1125 = 112.5 ≅ 112.
Population after 2 decades
= 1125 – 112 = 1013
Third decade’s population decrease
= 0.1 × 1013 = 101.3 ≅ 101.
Population after 3 decades
= 1013 – 101 = 912.
Rounding off, we can say that the expected population after 3 decades
will be around 910.
A provision store is offering a stock clearance sale. Customers can
choose one of the two options — 20% discount or ₹50 discount—for any
purchase above ₹150. Which option would you choose if you want to:
(i) buy items worth ₹180
(ii)
buy items worth ₹225
(iii) buy items worth ₹300
Example 12: A bakery called Cakely is
offering a 30% + 20% discount on all cakes.
Another bakery called Cakify is offering a
50% discount on all cakes. Would you rather
choose Cakely or Cakify if you want the
cheaper cost?
30% + 20% is the same as 50%, the usage of 30% + 20% in shopping means compounding.
Suppose you want to buy a cake worth ₹200.
→ Applying the 30% discount
→ the price of cake is ₹200 – ₹60 = ₹140.
Applying the 20% discount on ₹140
→ the price of cake is ₹140 – ₹28 = ₹112.
Cakify’s 50% → The 50% discount makes the price of the cake ₹100
Example 13: After Surbhi bought cookware from the wholesaler, she
kept a profit margin of 50% on all the products. To clear off the remaining
stock, she thought she would offer a 50% discount and come out without
any loss.
(i) Do you think she didn’t make any loss?
(ii) If she had sold goods (originally) for ₹12,000 after discount, how
much loss did she incur? What is the percentage loss?
(iii) What should have been the percentage discount offered so that she
sold the goods at the price she had bought (i.e., no profit
or loss)?
(i) This means the selling price is 3 /4 of the price the goods were bought
at, i.e., a 25% loss.
(ii) If she had sold goods worth ₹12,000,
0.75x = 12,000
x = 16,000.
She lost ₹4000.
(iii) To sell the goods at the same price, the discount offered should be
1.5x – d × (1.5x) = x
d = 1 /3 = 0.33.
The discount offered should have been 33.33%.
Ariba and Arun have some marbles. Ariba says, “The number of
marbles with me is 120% of the marbles Arun has”. What would be
an appropriate statement Arun could make comparing the number
of marbles he has with Ariba’s?
The number of marbles with me is 120% of the marbles Arun has.”
Step 1: Assume Arun’s marbles
Let Arun have 100 marbles (this makes percentage comparison easy).
Then Ariba has:
120% of 100=120
Step 2: Compare Arun’s marbles with Ariba’s
Arun has 100, Ariba has 120.
So Arun’s marbles as a percentage of Ariba’s:
Appropriate statement by Arun
“The number of marbles I have is 83⅓% of the marbles Ariba has.”
If one quantity is 120% of another,
the other is not 80% back — it must be calculated by division.
Figure it Out Page no 27 - 28
1. The population of Bengaluru in 2025 is about 250% of its population
in 2000. If the population in 2000 was 50 lakhs, what is the population
in 2025?
Answer: 125 lakhs (1.25 crore)
2. The population of the world in 2025 is about 8.2 billion. The
populations of some countries in 2025 are given. Match them with
their approximate percentage share of the worldwide population.
[Hint: Writing these numbers in the standard form and estimating
can help]
| Country | Population | % of world population |
|---|
| India | 1.46 billion | (\approx \frac{1.46}{8.2} \times 100 \approx 18%) |
| USA | 347 million = 0.347 bn | (\approx 4%) |
| Bangladesh | 175 million = 0.175 bn | (\approx 2%) |
| Germany | 83 million = 0.083 bn | (\approx 1%) |
Matching:
-
India → 18%
-
USA → 4%
-
Bangladesh → 2%
-
Germany → 1%
3. The price of a mobile phone is ₹8,250. A GST of 18% is added to
the price. Which of the following gives the final price of the phone
including the GST?
(i) 8250 + 18
(ii) 8250 + 1800
(iii) 8250 + 18
100
(iv) 8250 × 18
(v) 8250 × 1.18
(vi) 8250 + 8250 × 0.18
(vii) 1.8 × 8250
Price = ₹8250
GST = 18%
Correct expressions:
Correct options: (v) and (vi)
4. The monthly percentage change in population (compared to the
previous month) of mice in a lab is given: Month 1 change was +5%,
Month 2 change was –2%, and Month 3 change was –3%. Which of
the following statement(s) are true? The initial population is p .
(i) The population after three months was p × 0.05 × 0.02 × 0.03.
(ii) The population after three months was p × 1.05 × 0.98 × 0.97.
(iii) The population after three months was p + 0.05 – 0.02 – 0.03.
(iv) The population after three months was p.
(v) The population after three months was more than p.
(vi) The population after three months was less than p.
Changes:
-
Month 1: +5%
-
Month 2: −2%
-
Month 3: −3%
Correct method → successive multiplication
Correct statements:(ii), (vi)
5. A shopkeeper initially set the price of a product with a 35% profit
margin. Due to poor sales, he decided to offer a 30% discount on the
selling price. Will he make a profit or a loss? Give reasons for your
answer
Let CP = 100
Loss =
Result: Loss of 5.5%
Profit % and Discount % cannot be compared directly unless they are on the same base
6. What percentage of area is occupied by the region marked ‘E’ in the
figure?
The whole figure is drawn on a dot grid, so we can count equal unit squares.
-
The outer shape is a big rectangle, divided into regions A, B, C, D, E.
-
Region E is the triangular region at the bottom-left.
f 5?
What is 25% of 12? What is 12% of 25?
What is 15% of 60? What is 60% of 15?
What do you notice?
Can you make a general statement and
justify it using algebra, comparing x%
of y and y% of x?
Examples
5% of 40 = 2
40% of 5 = 2
25% of 12 = 3
12% of 25 = 3
15% of 60 = 9
60% of 15 = 9
Observation
The value of x% of y is always equal to y% of x.
Percentage is just multiplication by a fraction, and multiplication does not depend on order.
General statement x% of y = y% of x
Observation & General rule proven
x% of y=y% of xx\% \text{ of } y = y\% \text{ of } x8. A school is organising an excursion for
its students. 40% of them are Grade
8 students and the rest are Grade 9
students. Among these Grade 8 students, 60% are girls. [Hint:
Drawing a rough diagram can help].
D
B
E
C
(i) What percentage of the students going to the excursion are
Grade 8 girls?
(ii) If the total number of students going to the excursion is 160,
how many of them are Grade 8 girls?
Total students = 100%
-
40% are Grade 8
-
Remaining 60% are Grade 9
-
Among Grade 8, 60% are girls
Percentage of Grade 8 girls
Grade 8 girls=60100×40%=24%\text{Grade 8 girls} = \frac{60}{100} \times 40\% = 24\%
24% of the students are Grade 8 girls\boxed{24\% \text{ of the students are Grade 8 girls}}
Grade 8 students
40% of 160=40100×160=6440\% \text{ of } 160 = \frac{40}{100} \times 160 = 64Grade 8 girls
60% of 64=60100×64=38.460\% \text{ of } 64 = \frac{60}{100} \times 64 = 38.4So approximately:
38 (approximately) Grade 8 girls\boxed{38 \text{ (approximately) Grade 8 girls}}
(i) Percentage of Grade 8 girls:
40%×60%=24%40\% \times 60\% = 24\%(ii) Total students = 160
24%×160=38.4≈38 students
9. A shopkeeper sells pencils at a price such that the selling price
of 3 pencils is equal to the cost of 5 pencils. Does he make a
profit or a loss? What is his profit or loss percentage?
Let CP of 1 pencil = ₹1
CP of 5 = ₹5 → SP of 3 = ₹5
SP of 1 = ₹1.67
Profit = ₹0.67 per pencil
Profit %=0.671×100≈67%\text{Profit \%} = \frac{0.67}{1} \times 100 \approx 67\%
10. The bus fares were increased by 3% last year and by 4% this year.
What is the overall percentage price increase in the last 2 years?
Successive percentage increases → use multiplication, not addition.
Let the original bus fare be ₹100
After 1st year (3% increase)
100+3% of 100=100×1.03=103After 2nd year (4% increase)
103+4% of 103=103×1.04=107.12103 + 4\% \text{ of } 103 = 103 \times 1.04 = 107.12Overall Increase
Increase=107.12−100=7.12%
11. If the length of a rectangle is increased by 10% and the area is
unchanged, by what percentage (exactly) does the breadth decrease
by?
Area of a rectangle:
Area=Length×Breadth\text{Area} = \text{Length} \times \text{Breadth}
If area is constant, then:
This is inverse proportionality.
10% increase means:
New length=1+10100=1.1 times original length\text{New length} = 1 + \frac{10}{100} = 1.1 \text{ times original length}
So,
L→1.1LL \rightarrow 1.1L
Since area is unchanged:
L×B=(1.1L)×B′L \times B = (1.1L) \times B'
Cancel L:
B=1.1B′B = 1.1B'
B′=B1.1B' = \frac{B}{1.1}
π This is why you wrote:
Breadth=11.1\text{Breadth} = \frac{1}{1.1}
So the new breadth is 11.1\frac{1}{1.1} times the original breadth.
Original breadth = 1
New breadth = 11.1\frac{1}{1.1}1.11
Decrease:
1−11.11 - \frac{1}{1.1}
Convert 1 as 1.11.1\frac{1.1}{1.1}1.11.1:
1.1−11.1=0.11.1\frac{1.1 - 1}{1.1} = \frac{0.1}{1.1}
Step 5: Convert decrease into percentage
0.11.1×100\frac{0.1}{1.1} \times 100
=9.09%= 9.09\%Breadth decreases by 9.09%
12. The percentage of ingredients in a 65 g chips
packet is shown in the picture. Find out the
weight each ingredient makes up in this
packet.
Convert each percentage to grams:
Ingredient mass=%×65\text{Ingredient mass} = \% \times 65Ingredient mass=%×65
Total weight of chips packet = 65 g
Percentage composition:
Weight of ingredient=Percentage100×Total weight\text{Weight of ingredient} = \frac{\text{Percentage}}{100} \times \text{Total weight}
|
Ingredient
|
Percentage
|
Weight g
|
|
Potato
|
70%
|
70% of 65 = 45.5 g
|
|
Vegetable oil
|
24%
|
24% of 65 = 15.6 g
|
|
Salt
|
3%
|
3% of 65 = 1.95 g
|
|
Spices
|
3%
|
3% of 65 = 1.95 g
|
|
Total 100% 65g
|
|
|
|
13. Three shops sell the same items at the same
price. The shops offer deals as follows:
Shop A: “Buy 1 and get 1 free”
Shop B: “Buy 2 and get 1 free”
Shop C: “Buy 3 and get 1 free”
Answer the following:
(i) If the price of one item is ₹100, what is the effective price per
item in each shop? Arrange the shops from cheapest to costliest.
(ii) For each shop, calculate the percentage discount on the items.
[Hint: Compare the free items to the total items you receive.]
(iii) Suppose you need 4 items. Which shop would you choose? Why?
Three shops sell the same item at the same price ₹100 each.
They offer the following deals:
-
Shop A: Buy 1 and get 1 free
-
Shop B: Buy 2 and get 1 free
-
Shop C: Buy 3 and get 1 free
(i) Effective price per item
Shop A: Buy 1 Get 1 Free
-
Pay for 1 item = ₹100
-
Total items received = 2
Effective price per item=1002=₹50\text{Effective price per item} = \frac{100}{2} = ₹50Shop B: Buy 2 Get 1 Free
-
Pay for 2 items = ₹200
-
Total items received = 3
Effective price per item=2003≈₹66.67\text{Effective price per item} = \frac{200}{3} \approx ₹66.67Shop C: Buy 3 Get 1 Free
-
Pay for 3 items = ₹300
-
Total items received = 4
Effective price per item=3004=₹75\text{Effective price per item} = \frac{300}{4} = ₹75| Shop | Effective price per item |
|---|
| A | ₹50 |
| B | ₹66.67 |
| C | ₹75 |
(ii) Percentage discount
Discount %=Free itemsTotal items×100\text{Discount \%} = \frac{\text{Free items}}{\text{Total items}} \times 100
| Shop | Discount % |
|---|
| A | (\frac{1}{2} \times 100 = 50%) |
| B | (\frac{1}{3} \times 100 = 33.33%) |
| C | (\frac{1}{4} \times 100 = 25%) |
(iii) If you need 4 items, which shop is best?
-
Shop A: Buy 2 → Get 2 free → Pay ₹200
-
Shop B: Buy 4 → Get 1 free → Pay ₹400
-
Shop C: Buy 4 → Get 1 free → Pay ₹300
Best choice: Shop A (lowest cost)
14. In a room of 100 people, 99% are left-handed. How many
left-handed people have to leave the room to bring that
percentage down to 98%?
Total people in the room = 100
Left-handed people = 99% of 100 = 99
Right-handed people = 1
Let x left-handed people leave
Then:
Left-handed people remaining = 99 − x
Total people remaining = 100 − x
New percentage condition
Left-handed peopleTotal people=98%\frac{\text{Left-handed people}}{\text{Total people}} = 98\%
99−x100−x=981009−x100−x=4950\frac{99 - x}{100 - x} = \frac{49}{50} Cross multiply:
50(99−x)=49(100−x)50(99 - x) = 49(100 - x)
4950−50x=4900−49x4950 - 50x = 4900 - 49x
4950−4900=50x−49x4950 - 4900 = 50x - 49x
50=x50 = xAfter 50 left-handed people leave:
-
Left-handed = 49
-
Right-handed = 1
-
Total = 50
4950×100=98%\frac{49}{50} \times 100 = 98\%
15. Look at the following graph
Based on the graph, which of the following statement(s) are valid?
(i) People in their twenties are the most computer-literate among
all age groups.
(ii) Women lag behind in the ability to use computers across age
groups.
(iii) There are more people in their twenties than teenagers.
(iv) More than a quarter of people in their thirties can use computers.
(v) Less than 1 in 10 aged 60 and above can use computers.
(vi) Half of the people in their twenties can use computers
The graph shows percentage of people who can use computers by:
-
Age group
-
Gender (Male / Female)
(i) People in their twenties are the most computer-literate
True
Both male and female percentages are highest in the twenties group.
(ii) Women lag behind men in all age groups
True
In every age group, the male bar is higher than the female bar.
(iii) There are more people in their twenties than teenagers
False
The graph shows percentage, not population size.
We cannot compare how many people are there.
(iv) More than a quarter of people in their thirties can use computers
False
Combined (male + female) is below 25%.
(v) Less than 1 in 10 aged 60+ can use computers
True
Seniors show around 4–6%, which is less than 10%.
(vi) Half of people in their twenties can use computers
False
Male + female together ≈ 37%, not 50%.
Final Correct Statements
(i), (ii), (v)