answer
If y varies jointly as x and z and inversely as w, and y=25 when x=4, z=75 and w=6. Find y when x=6, z=50 and w=15.
The formula would be y=kxz/w where k is a constant and found by rearranging the equation to yield
k=y*w/(x*z) = 25*6/(4*75) = 25*3*2/(2*2*25*3) = 1/2
y=.5xz/w = .5*6*50/15 = 10
