Question

If y varies directly as x and y = 70 when x = 10, find y when x = 36.

252

2,520

25,200

5.14

Answer 1

252

Explanation:

y varies directly with x means y=kx where k is a constant.

A constant means it never changes no matter what the point (x,y) they give.

So y=kx means y/x=k (I just divided both sides by x here).

So we have the following proportion to solve:

`(y_1)/(x_1)=(y_2)/(x_2)`

`(70)/(10)=(y_2)/(36)`

70/10 reduces to 7:

`7=(y_2)/(36)`

Multiply both sides by 36:

`7(36)=y_2`

Simplify left hand side:

`252=y_2`

So y is 252 when x is 36.