A pet store sold 35 dogs. If the ratio of dogs sold to cats sold was 7:3, how
many cats were sold?

The direct variation says that:

then the equation is in the form of : y =kx.....[1] where k is the constant of variation.

From the table:

Consider any values of x and y.

Let x = 20 and y =24

Substitute these values in [1] to solve for k;

Divide both sides by 20 we get;

⇒

Check:

Substitute any values of x and y.

x= 30 and y =36

36 = 1.2(30)

36 = 36         True.

Therefore, the direct variation equation for the table of ordered pairs is,