Problem: A running track is the ring formed by two concentric circles. It is 101010 feet wide. The circumferences of the two circles differ by about
Answer Choices:
A. 101010 feet
B. 303030 feet
C. 606060 feet
D. 100100100 feet
E. none of these Solution:
C1=2Οr,C2=2Ο(r+10);β΄C2βC1=20ΟβΌ60C_{1}=2 \pi r, C_{2}=2 \pi(r+10) ; \quad \therefore C_{2}-C_{1}=20 \pi \sim 60C1β=2Οr,C2β=2Ο(r+10);β΄C2ββC1β=20ΟβΌ60 (feet).