Wvaries jointly as x and y and inversely as the square of z. if w = 280 when x = 30, y = 12, and. z = 3, find w when x = 20, y = 10 and z = 2.

The joint variation of W with x, y and z may be expressed as follow,
                                    W = kxy / z²
where k is the constant of variation. Substituting the first set of values for the variables,
                                   280 = k(30)(12) / 3²
The value of k from the equation is 7. Substituting to the same equation the values of the next set of variables,
                                      w = (7)(20)(10) / 2² = 350
The answer is 350.