Question

If y varies directly with x and y=21 when x=7, how do you find y when x=-1.66?

Answer 1

`y=-4.98`

Explanation:

This statement means `y propx`, which can also be written in the form `y=kx` when it is directly proportionate and `y=k/x`when inversely proportionate, where `k` is a value we need to work out.

Since the equation is in the form `y=kx` we know that...

`21=K xx 7`

`therefore` `k=21/7=3`.

So we can write this as the formula:

`y=3x`

Therefore using the value of `x=-1.66`

`y=3x -> y=3xx -1.66=-4.98`