Grade 7 - Mathematics 9.11 The Area of a Circular Path - III

Example:
The area of circular park is 2464 square metres. A path of width 7 metres is laid around and inside of it. Find the area of the path.

Solution:
The area of the circular part of the outer ring. Let its radius be R metres.
So, pR^{2} = 2464
R^{2} = 7/22 * 2464
R^{2} = 7 * 112
R^{2} = 784
Taking square root on both sides.
R = 28
Let the radius of the inner ring be r metres.
Therefore, R - r = 7
So, r = R - 7
r = 28 - 7
r = 21
Therefore, the area of the circular path = p(R + r)(R - r)
= 22/7 * 49 * 7
= 12166/7
= 1738 square metres.

Directions: Read the above example carefully and answer the following questions. Also write 10 examples of your own.