In a 100 m race, A can give B a start of 10 m and C a start of 28 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 90 m and C runs 72 m.

2. 02

   So when B runs 100 m, C runs $72 \times \frac{100}{90} = 80$ m: B can give C 20 m.