Question

If a ∝ b and a = 18 when b = 3, then find a when b = 5.

Answer 1

"a ∝ b" means "a is proportional to b", which in turn means there is some constant k such that

a = kb

We're given that a = 18 and b = 3, so that

18 = 3k   ⇒   k = 6

Then when b = 5, we would have

a = 6 × 5 = 30