Writing a direct variation equation

Question

Suppose that y varies directly with x, and =y 5 when =x20.

Then it asks for:

(a): Write a direct variation equation that relates x and y.

(b): Find y when x=8

y= ____

Answer 1

y = kx = f(x)

5 = k(20) <--- y=5 when x=20

Solves for k:

k = 5/20 = 1/4

So the function is

y = (1/4)x = f(x)

Part B:

f(8) = (1/4)*8 = 2, so y=2 when x=8