Question

If y varies directly as x, and y = 6 when x= 3, find y when x = 9.
y =when x= 9.

Answer 1

We know that:

- y varies directly as x

- y = 6 when x= 3

And we must find y when x = 9

To find it:

1. we must use that y varies directly as x

`y=kx`

2. We must find k using that y = 6 when x = 3

`\begin{gathered} 6=k\cdot3 \\ k=(6)/(3) \\ \Rightarrow k=2 \end{gathered}`

3. Finally, to find y when x = 9 we must replace x = 9 and k = 2 to solve it for y

`\begin{gathered} y=2\cdot9 \\ y=18 \end{gathered}`

ANSWER:

y = 18 when x = 9