If y varies directly with x, and y=20 when x=4, find the value of y when x=3

Question

If y varies directly with x, and y=20 when x=4, find the value of y when x=3

Answer 1

Our basic problem looks like:

y = qx

 

When we plug in our variables, we get:

20 = q * 4

 

To isolate q, we divide both sides by 4:

20 / 4 = q * 4 / 4, which becomes:

5 = q, leading to 5x = y

 

now to plug in our 3 variable:

5 * 3 = 15 = y