If y is 5 when x is 2.5 and y varies directly with x, find y when x is 10.
5
7.5
12.5
20

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

Y varies directly with x
y = kx

Plug in x = 2.5, and y = 5

5 = 2.5k
k = 2

y = 2x

Find y when x = 10

y = 2(10)
y = 20

y is 20 when x is 10.