Question

The variables x and y are directly proportional, and y = 2

when x = 3. What is the value of y when x = 9 ?

Answer 1

Direct proportionality:

`y=kx`
k - the constant of proportionality


`y=2 \hbox{ when } x=3 \\ \Downarrow \\ y=kx \\ 2=3k \\ k=(2)/(3) \\ \\ y=? \hbox{ when } x=9 \\ \Downarrow \\ y=kx \\ y=(2)/(3) * 9 \\ y=2 * 3\\ y=6 \\ \\ \boxed{y=6 \hbox{ when } x=9}`