Question

If y varies directly with x, and If y = -16 when x = 4, how do you find x when y = 20?

Answer 1

When `y =20` , `x` is `color(Blue)(-5`

Explanation:

`y` varies directly with `x` this implies `y` is directly proportional to `x`:
`color(blue)(y prop x`

Upon introducing constant `k` (constant of proportionality ):
`y = color(green)(k) x`........`(1)`

As per given data: when `y=-16, x=4`, substituting the above values in `(1)` to find `color(green)(k`

`-16 = k xx 4`

`k = -16/ 4`

`color(green)(k = -4`,

Finding `x` when `color(blue)(y =20` :

`y=kx`

`color(blue)(20) = color(green)(-4) xx x`

`x = 20/ (-4)`

`color(blue)(x= -5`