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 22
2. Find the circumference and area of circles of the following radius. Take π= 7  
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(a) 7 cm (b) 3.5 cm (c) 56 mm (d) 1.4 m

3. Find the circumference and area of the circle of diameter 56 cm.
4. Find the area of a circle whose circumference is 66 cm.
5. The radius of a semicircle is 7 cm. Find its circumference and area.
6. The diameter of a wheel of a bicycle is 63 cm. How many revolutions will it make to travel 13.86 km?

7. The ratio of the radii of two circles is 7 : 9. What is the ratio of their circumferences?
8. A piece of a wire in the form of rectangle 15.1 cm long and 11.3 cm broad is reshaped and bent into
the form of a circle. Find the circumference and area of the circle.
9. A race track is in the form of a ring whose inner circumference is 528 m and the outer circumference
is 616 m. Find the width of the track.
10. A circular grassy plot of land, 56 m in diameter, has a path 2.1 m wide running around it on the
outside. Find the cost of gravelling the path at ₹5.50 per square metre.
2
11. The area of a circular garden is 9856 m . Outside this garden, a path of uniform width is laid all
2
around. The area of the path is 2618 m . Find the radius of the circular garden and width of the path.

A Pinch of History

Pi (p) has been known for almost 4000 years—but even if we calculated the number of seconds
in those 4000 years and calculated p to that number of places, we would still only be

approximating its actual value.
Since, the Indus Valley script is not deciphered, it would be

incorrect to claim that p was known in the subcontinent in
3000 BCE. But they did know the value of p by the time Rigveda
was written. The Vedangas and Sulabasutras also mention the

value of p. The oldest of them, the Baudhayayana Sulabasutra
claims that the perimeter of a pit is 3 times its diameter.
Therefore, approximating the value of p at 3. Many other
texts, including the Mahabharata (Bhishmaparva, XII: 44) and

many Puranas approximate p at the value of 3.
62832
Later on Aryabhata discovered an approximation of p, = 3 1416.
.
20000

299 Perimeter and Area