Math Homework. Do It Faster, Learn It Better.

Joint Variation

Joint variation describes a situation where one variable depends on two (or more) other variables, and varies directly as each of them when the others are held constant. We say z varies jointly as x and y if


for some constant k .


If z is jointly proportional to x and y and z=6 , when x=3 and y=4 , find z when x=7 and y=4 .

Find k :

6=3( 4 )k

k= 1 2

Then, find z when x=7 and y=2 .

z= 1 2 ( 7 )( 2 ) z=7