Question

y varies directly with x. if y =20 when x=4, what is y when x=2?

Answer 1

If y varies directly with x, this means that each time x increases one unit, y gets modified k times:

You can symbolize this as

$y=kx$

When y=20, x=4, with this you can determine the value of k as:

$\begin{gathered} 20=4k \\ k=\frac{20}{4} \\ k=5 \end{gathered}$

k=5 means that every time x increases one unit, y will increase 5 units.

$y=5x$

Now you can calculate the value of y for x=2 as

$\begin{gathered} y=5\cdot2 \\ y=10 \end{gathered}$

When x=2, y=10