Question

If y varies directly as x, what is the value of y in (4,16) and (2,y)

Answer 1

Y varies directly with x means y = kx or y/x = k where k is the constant of variation (slope)

Using $\frac{y}{x} = \frac{y}{x}$ we can plug in the x and y values from the given points.

We get the following proportion:
$\frac{16}{4} = \frac{y}{2}$
32 = 4y ← cross multiply
8 = y ← divide both sides by 4

ANSWER: y = 8