Write a direct varaition equation that relates x and y

Question

Suppose y varies directly with x, and Y equals 15 and x equals 5. Write a direct variation equation that relates X and Y. What is the value of y when x equals 9?

Answer 1

Suppose y varies directly with x,

y∝ x

y=kx  where k is constant of variation.

y=15,x=5

 15 = 5k

  k=15/5

  k=3

y=3x

x=9, y=3*9=27