Question

If y varies directly as x, and y = 15 as x = -3, find y for the x-value of 4.

Answer 1

Direct variation takes the form y=kx.
to find k, plug in the given values:
15 = k(-3)
k = -5
now you have y = -5x, so plug in 4 for x to find y:
y = -5(4) = -20

inverse variation takes the form y=k/x.
find k:
5 = k/6
k = 30
formula: y = 30/x
when x=10:
y = 30/10 = 3