In a 100 m race, A can give B a start of 20 m and C a start of 30 m. How much of a start can B give C in a 100 m race?

Explanation

1. 01

   While A runs 100 m, B runs 80 m and C runs 70 m, so B : C = 80 : 70.

2. 02

   While B runs 100 m, C runs $\frac{70}{80} \times 100 = 87.5$ m, so B can give C a start of 12.5 m.