Question

If a varies directly as b, and a = 28 when b = 7, find b when a = 5.

Answer 1

ratio is 28/7 which is equal to 4/1
so now cross multiply:
4/1 = 5/b
1 * 5 = 5
4 * b = 5
4 * 1.25 = 5
so b = 1.25 when a = 5

Answer 2

Hope this helps!