Question

Points A, B, and C lie on line segment AC. The ratio of AB:BC is 3:7, and the length of AC = 120. What is the length of BC?

Answer 1

In terms of "ratio units," the length of AC is 3+7=10, so each one is worth 120/10 = 12. The length BC is 7 of those, or 7·12 = 84.

Answer 2

The ratio of AB:BC is 3:7
3 + 7 = 10
 the length of AC = 120
so 120 / 10 = 12

BC = 7 x 12 = 84

Answer
The length of BC = 84