Joint variations occurs when one variable depends on the value of two or more variables. The variable varies directly or indirectly with the other variables combined together. The other variables are held constant. From the given examples, the equation(s) that represent joint variations are
1) z = 3x/y
z varies directly with x and inversely with y.
2) w = abc/4
w varies inversely with a,b and c. 4 is the value of the constant of variation.
