If Z varies directly as X and inversely as Y, and Z = 9, when X = 5 and Y = 3, find X when Z = 18 and Y = 6

Answer 1

"If Z varies directly as X and inversely as Y" ---> z =k(x/y)

when z=9, x=5,y=3
9 = k(5/3)
5k = 27
k = 27/5

So we have z = (27/5)(x/y)

for z=18, y = 6
18 = (27/5)(x/6)
27x = 540
x = 20