Page 135 - Maths Skills - 7

Perimeter and Area 133

Example 4: The distance covered by a wheel in one revolution is 88 cm, find the diameter of the wheel.

Solution: Distance covered by a wheel in one revolution = circumference of circular wheel = 88 cm
C
As C = pd ⇒ d =
p
88 × 7
⇒ d = 22 cm or d = 28 cm

Example 5: The perimeter of a rectangular sheet is 100 cm if its length is 40 cm, find its breadth.
Solution: Perimeter of rectangular sheet = 100 cm, Length (l ) of the sheet = 40 cm

Perimeter = 2(l + b) = 100 cm

⇒ 2(40 + b) = 100

⇒ 40 + b = 50

⇒ b = 50 – 40 = 10 cm

Exercise 8.1

1. Find the perimeter of the following figures.

10 cm
5 cm 5 cm

10 cm

2. Find the circumferences of the circles whose diameters are.
(i) 14 cm (ii) 42 m (iii) 63 m (iv) 21 cm

3. Find the perimeter of a square of side 3 cm.
4. A square piece of field has each side equal to 150 m. If 3 layers of barbed wire has to be used to fence it,
what is the length of the wire required? Also find the total cost of the wire if a metre of wire costs ` 2.

5. A wire in the form of a square of side 11 cm each is reshaped and bent into the form of a circle. Calculate
the diameter of the circle so formed.
6. Find the distance covered by a wheel of radius 1.4 m, if it makes 250 revolutions.
7. Find the perimeter of a rectangle of length 12 cm and breadth 5.5 cm. What will be the length of the side
of a square with same perimeter as that of a rectangle?

8. Find the circumferences of the circles whose radii are:
(i) 3.5 cm (ii) 7 cm (iii) 0.14 m (iv) 6.23 m

9. The distance covered by a wheel in 5 revolutions is 220 m. Find the diameter of the wheel.

10. The length of a rectangular field is twice its breadth. Arun jogged around it 3 times and covered a
distance of 5.4 km. Find the length and breadth of the field?