Question

Suppose y varies directly as x, and y= 3 when x = 7.5. Find y when x = 18.

Answer 1

`y\propto x`

y = k; k is variation constant

we have:

y = 3 when x = 7.5

`\begin{gathered} 3=k*7.5 \\ (3)/(7.5)=(k*7.5)/(7.5) \\ k=(3)/(7.5)\text{ or k=}(2)/(5)\text{ or k = 0.4} \end{gathered}`

thus the variation equation is

`y=0.4* x`

then, when x=18

`\begin{gathered} y=0.4*18 \\ y=7.2 \end{gathered}`