Question

Suppose that for a particular relation, `y` varies directly as `x` and that when `x=3` then `y=15`. What is the value of `y` when `x=12`?

Answer 1

`y=60`

Explanation:

If `y` directly varies as `x`, then
`color(white)("XXX")y=kx`, for some constant `k`.

You then substitute in the numbers:
`color(white)("XXX")15=k * 3`
Therefore, `5=k`

Put that into the original equation:
`color(white)("XXX")y=5x`

Substitute in `12` for `x`
`color(white)("XXX")y=5 * 12`
Therefore,
`color(white)("XXX")y=60`