If y varies directly as x and if y=12 when x=4, find y when x=40

Answer 1

Direct variation uses the form:

y = k(x).

First, we use the given information to solve for k:

12 = k(4)

k = 3

Then, we rewrite the equation with our value of k plugged in:

y = 3x

Finally, we plug in x = 40 and solve for y:

y = 3(40)

y = 120