Question

An outside circular ring has a circumference of 200 cm. What is the circumference of an inner ring which is 25 cm shorter in radius? Both circles have the same center.

Answer 1

find circumferences

c=2pir
200=2pir
divide by 2
100=pir
divide by pi
100/pi=r
aprox
31.83099=r
25 les than that is
6.83099
c=2pir
c=2*3.141592*6.83099
c=42.9204
about 43cm

Answer 2

First, find the circumference of the outer ring. The formula to be used is

C = 2*pi*r
200 = 2*pi*r
r = 31.83 cm

Since, both rings are concentric, just subtract 25 from the radius of the outside ring to find the radius of the inner ring

radius of inner ring = 31.83 - 25
radius of inner ring = 6.83

Then, we use this radius to the formula to find its circumference:

C = 2*pi*6.83
C = 42.91 cm