Question

If `y=-2` when `x=4`, what is `x` when `y=5`?

`y` varies directly as `x`.

Answer 1

`x=-10`

Explanation:

Since `y` varies directly with `x`, that means that:

`y/x=`some number. In other words, they have the same ratio.

To solve for `x`, figure out when the ratios equal each other. We'll use:

`y_1/x_1=y_2/x_2`

Plug into the formula:

`-2/4=5/x`

Cross multiply:

`-2x=20`

Divide `-2` on both sides to solve for `x`:

`(-2x)/-2=20/-2`

This results in:

`x=-10`