Question

If y varies directly with x and y = 90 when x = 15 then what is y when x =4?

Answer 1

y = 24

Step-by-step explanation:

Given;

x = 15 when y = 90

Also y varies directly with x

i.e y ∝ x

Introduce a constant k.

y = kx

Let k be the constant.

First solve for K:

`\begin{gathered} y\text{ = kx} \\ \\ 90\text{ = 15k} \\ \text{Divide both sides by 15:} \\ (90)/(15)=(15k)/(15) \\ 6\text{ = k} \end{gathered}`

Substitute 6 for k in the equation y =kx

Thus, we have:

y = 6x

Therefore, when x = 4, y will be:

`\begin{gathered} y\text{ = 6 }\ast\text{ 4} \\ \\ \text{ y = }24 \end{gathered}`

when x =4, y = 24