Y varies jointly as x and z. If y=5 when z=4 and x=2, find y when x=6 and z=8.

In the second example, y = 30.

In order to find this, we must find the coefficient that goes along with the joint variation. When we look for joint variation, we can express it by showing the number numbers being multiplied by each other and a third unknown numbers. Thus we have the below equation.

y = Cxz

So to find the coefficient (C), just plug in and solve using the first sets of numbers.

y = Cxz

5 = C (4) (2)

5 = 8C

5/8 = C

Now we can use that number to create the following equation.

y = 5/8xz

And we can plug into that to find our last y value.

y = 5/8xz

y = 5/8 (6) (8)

y = 30