if y is 5 when x is 2.5 and y varies directly with x, find y when x is 10.
The term "y varies directly with x" means that the formula is a direct variation. We need to look for the constant of variation.
y = kx ; where k is the constant of variation.
k = y/x
k = 5/2.5
k = 2
We then use the direct variation formula to get the value of y when x is a certain number.
y = kx
y = 2 * 10
y = 20
