In a 100 m race, A beats B by 10 m and C by 13 m. In a race of 180 m, B will beat C by:

A : B = 100 : 90.

A : C = 100 : 87.

When B runs 30 m, C runs 29 m.

When B runs 180 m, C runs		29	x 180	m	= 174 m.
		30

 B beats C by (180 - 174) m = 6 m.