Question

If y varies directly with x and y = -4.5 when x = 13.5, how do you find x when y = 24?

Answer 1

`x = 72`

Explanation:

If `color(red)(y)` varies directly with `color(blue)(x)` then
`color(white)("XXX")color(red)(y) =c*color(blue)(x)` for some constant `c`

We are told
`color(white)("XXX")color(red)(-4..5) = c*color(blue)(13.5)`

`rarrcolor(white)("X")c = color(red)(-4.5)/color(blue)(13.5) = -1/3`

When `color(red)(y)=color(red)(24)`
`color(white)("XXX")color(red)(24) = (-1/3)color(blue)(x)`

`rarrcolor(white)("X")color(blue)(x) = color(red)(24)*(-3) = 72`