A running track is the ring formed by two concentric circles. If the circumferences of the two circles differ by 20 pi feet, how wide is the track in feet?
The circumference of the inside circle can be expressed as 2pi R1
The circumfernce of the outside circle can be expressed as 2piR2
20pi = 2pi R2 - 2pi R1
20pi = 2pi (R2 - R1) divide both sides by 2 pi
10 = R2 - R1 [ the track is 10 ft wide ]