Question

suppose x varies directly with y. when x= 12, y = 9. what is y when x = 28?

Answer 1

Given :

x varies directly with y.

So, the relation between them will be :

$y=k\cdot x$

Where x is the constant of proportionality

Given x = 12 when y = 9 , the constant k will be :

$\begin{gathered} 9=k\cdot12 \\ k=\frac{9}{12}=\frac{3}{4} \end{gathered}$

So, the relation will be :

$y=\frac{3}{4}x$

We need to find y when x = 28

So, substitute with x = 28

$\begin{gathered} y=\frac{3}{4}\cdot28 \\ \\ y=21 \end{gathered}$