Question

The diameters of two circles with centre A and B are 16cm and 30cm respectively. If the area of a circle with centre C is equal to the difference of areas of other two circles, then find the circumference of the circle with centre C.

Answer 1

First find areas of circles A & B

radius A = 16/2 = 8cm
radius B = 30/2 = 15cm

area A = 22/7 x 8 x 8
            = 201.14 cm square

area B = 22/7 x 15 x 15
            = 707.14 cm square

diff in area = 707.14 - 201.14
                  = 506

find radius of C = 22/7 x r^2 = 506
                         r^2 = 161
                         r = sq.root of 161

circumference = 2 x 3.14 x √161
                        = 6.28√161