Suppose j varies jointly with g and v, and j=1 when g=6 and v=3.

Find the constant variation and find j when g=8 and v=11

"Joint variation " means "directly, but with two or more variables". Thus, we write as follows:

j α gv

We insert proportionality constant k, to change it to equality.

j = kgv

We solve k,

1 = k (4) (3)

k = 1/12

j = gv/12

j = 8 (11) / 12

j = 22/3