Page 174 - Start Up Mathematics_5

EXERCISE 13.1

1. Find the perimeter of the rectangles whose dimensions are given below.
(a) length = 8 cm, breadth = 5 cm (b) length = 11 cm, breadth = 7 cm

(c) length = 15 cm, breadth = 12 cm (d) length = 20 cm, breadth = 16 cm
2. Find the perimeter of the squares whose dimensions are given below.

(a) side = 8 cm (b) side = 12 cm (c) side = 14 cm

(d) side = 18 m (e) side = 21 m (f) side = 16 cm
3. Find the perimeter of the triangles whose dimensions are given below.

(a) a = 4 cm, b = 5 cm, c = 6 cm (b) a = 8 cm, b = 11 cm, c = 13 cm

(c) a = 14 cm, b = 16 cm, c = 18 cm (d) a = 21 m, b = 23 m, c = 30 m
4. Find the side of the squares whose perimeters are given below.

(a) 64 cm (b) 96 cm (c) 112 cm (d) 144 cm (e) 168 cm

Area

Area is the surface covered by a plane figure. Area is measured in square units, i.e., the unit
of area is square cm or square m or any other square unit.

Consider a square of side 2 cm. We divide it into 4 equal squares as shown. The area of this
square is 4 square centimetre or 4 cm .
2

2 cm 1 1 Remember

1 I II 1 The units used to measure
2 cm 2 cm area are:
small areas: cm 2
1 IV III 1 large areas: m 2
2 cm 1 1 very large areas: km 2

Finding area by counting squares

To find the area of any plane object, place the object on a squared sheet of paper and count
the total number of squares covered by it.

Example 5: Find the area covered by the eraser. The area of each
square in the grid is 1 cm .
2
ERASER
Solution: There are 8 complete squares covered by the eraser.

8 × 1 cm = 8 cm 2
2
So, the area of the eraser is 8 square centimetre or 8 cm .
2

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