Question

Assume that y varies directly as x then solve. If x = 12
when y = 15 find x when y = 21.

Answer 1

18 or 16.8

Explanation:

if x=12 and y=15, this can be written as y=x+3 or y=1.25x

so your equation becomes x+3=21 or 1.25x=21

subtract 3 from both sides, or divide by 1.25

and you get x=18 or x=16.8

Answer 2

18

Explanation:

12 and 15 are both dividable by 3 and 3 apart so if you subtract 21 by 3 than you get 18