Perimeter = length of the boundary. Rectangle: 2 × (l + b). Square: 4 × side. Triangle: sum of the three sides. Regular polygon: number of sides × side.
Area = region enclosed, in square units. Rectangle: l × b. Square: side × side.
Odd shapes: split into rectangles (add) or box-and-subtract.
A triangle drawn inside a rectangle on the same base = half the rectangle.
Same area can have different perimeters (and the other way round). Long thin → more perimeter; square-like → less.
๐ Textbook Page 129
๐ Page 129Perimeter of a rectangle
Find the perimeter of rectangle ABCD with length 12 cm and breadth 8 cm.
Rectangle ABCD
1Perimeter = AB + BC + CD + DA.
2Opposite sides are equal, so perimeter = 2 × (length + breadth).
3= 2 × (12 + 8) = 2 × 20 = 40 cm.
✅ Answer: 40 cm
⚠️ Common mistake: Adding only two sides (12 + 8 = 20). The boundary has four sides.
๐ Textbook Page 130
๐ Page 130Perimeter of a square
Debojeet puts coloured tape all around a square photo frame of side 1 m. How much tape does he need?
A square photo frame of side 1 m with tape all around.
1Tape all around = perimeter of the square.
2All four sides are equal: 4 × 1 m = 4 m.
✅ Answer: 4 m
๐ Textbook Page 131
๐ Page 131Perimeter of a triangle
Find the perimeter of a triangle with sides 4 cm, 5 cm and 7 cm.
Triangle with sides 4 cm, 5 cm, 7 cm.
1Perimeter of a triangle = sum of its three sides.
24 + 5 + 7 = 16 cm.
✅ Answer: 16 cm
๐ Page 131Example · Lace on a tablecloth
Akshi puts lace all around a tablecloth 3 m long and 2 m wide. How much lace is needed?
1Lace all around = perimeter.
22 × (3 + 2) = 2 × 5 = 10 m.
✅ Answer: 10 m
๐ Page 131Example · Rounds of a park
Usha takes three rounds of a square park of side 75 m. How far does she walk?
1One round = 4 × 75 = 300 m.
2Three rounds = 3 × 300 = 900 m.
✅ Answer: 900 m
๐ Textbook Page 132
๐ Page 132Figure it Out · Q1
Find the missing terms: (a) perimeter of rectangle 14 cm, breadth 2 cm, length = ? (b) perimeter of square 20 cm, side = ? (c) perimeter of rectangle 12 m, length 3 m, breadth = ?
1(a) length + breadth = 14 ÷ 2 = 7, so length = 7 − 2 = 5 cm.
2(b) side = 20 ÷ 4 = 5 cm.
3(c) length + breadth = 12 ÷ 2 = 6, so breadth = 6 − 3 = 3 m.
✅ Answer: (a) 5 cm (b) 5 cm (c) 3 m
๐ก Tip: Halve the perimeter first — that gives length + breadth.
๐ Page 132Figure it Out · Q2
A rectangle with sides 5 cm and 3 cm is made of wire. The wire is bent into a square. What is the side of the square?
1Length of wire = perimeter of rectangle = 2 × (5 + 3) = 16 cm.
2Same wire makes the square: side = 16 ÷ 4 = 4 cm.
Wire 16 cm longSame wire bent into a square of side 4 cm
✅ Answer: 4 cm
๐ Page 132Figure it Out · Q3
A triangle has perimeter 55 cm and two sides 20 cm and 14 cm. Find the third side.
120 + 14 = 34 cm.
2Third side = 55 − 34 = 21 cm.
✅ Answer: 21 cm
๐ Page 132Figure it Out · Q4
Find the cost of fencing a rectangular park 150 m long and 120 m wide at ₹40 per metre.
1Perimeter = 2 × (150 + 120) = 2 × 270 = 540 m.
2Cost = 540 × 40 = ₹21,600.
✅ Answer: ₹21,600
๐ Page 132Figure it Out · Q5
A string 36 cm long is used to make (a) a square (b) an equilateral triangle (c) a regular hexagon. Find the length of each side.
1(a) 36 ÷ 4 = 9 cm.
2(b) 36 ÷ 3 = 12 cm.
3(c) 36 ÷ 6 = 6 cm.
✅ Answer: (a) 9 cm (b) 12 cm (c) 6 cm
๐ Page 132Figure it Out · Q6
A field 230 m long and 160 m wide is fenced with 3 rounds of rope. Find the total length of rope.
Field 230 m × 160 m fenced with 3 rounds of rope.
1One round = 2 × (230 + 160) = 2 × 390 = 780 m.
2Three rounds = 3 × 780 = 2340 m.
✅ Answer: 2340 m
๐ Textbook Page 133
๐ Page 133Matha Pachchi · Q1
Akshi runs 5 rounds of the outer track (70 m × 40 m). Find her total distance.
Two rectangular tracks; both girls start at the bottom-right corner.
1One round = 2 × (70 + 40) = 220 m.
25 rounds = 5 × 220 = 1100 m.
✅ Answer: 1100 m
๐ Page 133Matha Pachchi · Q2
Toshi runs 7 rounds of the inner track (60 m × 30 m). Find her distance. Who ran more?
1One round = 2 × (60 + 30) = 180 m.
27 rounds = 7 × 180 = 1260 m.
31260 m > 1100 m.
✅ Answer: Toshi ran 1260 m — she ran 160 m more than Akshi.
๐ Page 133Matha Pachchi · Q3
Mark A, B, C where Akshi is after 250 m, 500 m and 1000 m, and X, Y, Z where Toshi is after 250 m, 500 m and 1000 m. How many full rounds after 1000 m?
1Both start at the bottom-right corner and run along the bottom side first (as the arrows show).
2Akshi (220 m a round): 250 = 220 + 30 → A is 30 m along the bottom side.
3500 = 2 × 220 + 60 → B is 60 m along the bottom side.
41000 = 4 × 220 + 120 → 4 full rounds; 120 = 70 (bottom) + 40 (left side) + 10 → C is 10 m along the top side.
5Toshi (180 m a round): 250 = 180 + 70 = 60 (bottom) + 10 → X is 10 m up the left side.
6500 = 2 × 180 + 140 = 60 + 30 + 50 → Y is 50 m along the top side.
71000 = 5 × 180 + 100 = 60 + 30 + 10 → 5 full rounds; Z is 10 m along the top side.
A, B, C: Akshi after 250 m, 500 m, 1000 m. X, Y, Z: Toshi after 250 m, 500 m, 1000 m.
✅ Answer: Akshi: 4 full rounds by 1000 m; Toshi: 5 full rounds. See the marked points.
๐ก Tip: Take away full rounds first; then walk the leftover metres side by side.
๐ Textbook Page 134
๐ Page 134Deep Dive · Common finishing line
Square tracks: inner 100 m a side, outer 150 m a side. The finishing line is at the middle of the bottom side. For a 350 m race, where should A (inner) and B (outer) start?
Two square tracks with a common finishing line in the middle of the bottom side.
1Inner round = 4 × 100 = 400 m. Running 350 m to the line = starting 400 − 350 = 50 m ahead of the line (in the running direction).
2The line is 50 m from the bottom-right corner → A is at the bottom-right corner of the inner track.
3Outer round = 4 × 150 = 600 m. Start 600 − 350 = 250 m ahead of the line.
4From the line: 75 m to the corner + 150 m up the right side = 225 m; 25 m more along the top → B is 25 m from the top-right corner.
A: inner start (corner, 50 m before the line along the track direction reversed). B: outer start (25 m from the top-right corner).
✅ Answer: A: bottom-right corner of the inner track. B: on the top side of the outer track, 25 m from the top-right corner.
๐ Page 134Estimate and Verify
Cut a few random shapes from paper. Estimate each perimeter, then measure with a thread and a scale.
1Lay a thread along the boundary, mark the end, straighten it and measure.
2Compare with your estimate; estimates get better with practice.
✅ Answer: Activity — answers depend on your shapes.
๐ Page 134Akshi or Toshi?
On a dot grid a right triangle has two sides of 3 units and a slanting side. Akshi says the perimeter is 9 units; Toshi says it is more. Who is right?
The triangle on a dot grid.
1The two straight sides are 3 + 3 = 6 straight units.
2The slanting side crosses 3 dot squares diagonally: each diagonal is longer than a straight unit.
3So the perimeter is 6s + 3d, which is more than 9 units.
✅ Answer: Toshi is right: perimeter = 6s + 3d, more than 9 units.
๐ Textbook Page 135
๐ Page 135Straight and diagonal units
Write the perimeters of the purple, pink, green and brown shapes using straight (s) and diagonal (d) units.
Purple, pink, green and brown shapes on a dot grid.
1Count the red (straight) and blue (diagonal) edges of each shape.
Areas found by splitting into rectangles and triangles.
✅ Answer: a 24 · b 30 · c 48 · d 16 · e 12 sq units
๐ก Tip: Box-and-subtract: draw the smallest rectangle around the shape, then take away the right triangles at the corners.
๐ Textbook Page 145
๐ Page 145Making it More or Less
Using 9 unit squares: (1) smallest perimeter? (2) largest? (3) make perimeter 18. (4) Is each shape unique?
1(1) The 3 × 3 square is the most compact → 12 units.
2(2) Each square joined to the next by only one side → a line or any ‘snake’ → 20 units.
3(3) Each extra shared side cuts 2 units from 20. Make one 2 × 2 block with a tail of 5 squares → 18 units.
4(4) 12: only the 3 × 3 square. 20 and 18: many shapes (any line, L or snake gives 20; many shapes give 18).
✅ Answer: (1) 12 (2) 20 (3) e.g. a 2 × 2 block with a tail of 5 squares (4) only 12 is unique.
๐ Page 145Adding a square
A figure has perimeter 24 units. A new square is attached as shown. What happens to the perimeter? Can you make it increase, decrease or stay the same?
Perimeter = 24 units
1Each new square adds 4 sides but hides 2 sides for every side it shares.
2In the corner shown it touches 2 squares: +4 − 4 = 0 → stays 24.
A page with a border 1 cm from top and bottom, 1.5 cm from the sides.
✅ Answer: Page perimeter − 10 cm (for a 20 cm × 28 cm page: 86 cm).
๐ Page 149Figure it Out · Q7
Draw a 12 × 8 rectangle. Inside it, without touching, draw a rectangle with exactly half the area.
1Big area = 96, half = 48.
248 = 8 × 6 fits inside with space on all sides (12 > 8, 8 > 6).
An 8 × 6 rectangle (48 sq units) inside a 12 × 8 rectangle (96 sq units).
✅ Answer: e.g. an 8 × 6 rectangle (48 sq units).
๐ Page 149Figure it Out · Q8
A square is folded in half and cut into two rectangles. Which statement is always true? (a) each rectangle has more area than the square (b) the square’s perimeter is more than both rectangles’ together (c) both rectangles’ perimeters together = 1½ times the square’s (d) the square’s area is 3 times both rectangles’ together
1Take side 4: square perimeter 16, area 16.
2Each rectangle 4 × 2: perimeter 12; together 24.
324 ÷ 16 = 1½. True for any size: together = 6 × side, square = 4 × side.
4(a) false (each is half). (b) false (24 > 16). (d) false (areas are equal).
A square of side 4 cut into two 4 × 2 rectangles.
✅ Answer: (c)
๐ Where do we use this?
Fencing, lace, tiles, carpets, painting walls, house plans, sports tracks.
๐ Link to higher classes
Class 7: area of parallelograms and triangles (½ × base × height). Class 8: area of trapeziums and circles.
CHAPTER 2 - Power Play nแต is n × n × n × n × ... × n (n multiplied by itself a times) and n⁻แต = 1 n a . nแต × nแต = nแต⁺แต (nแต)แต = (nแต)แต = n...
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