Question

The variable z is directly proportional to x, and inversely proportional to y. When x is 9 and y is 12, z has the value 15. What is the value of z when x= 17, and y= 16?

Answer 1

zαx/y
z=kx/y
thus
k=zy/x
where:
k=constant of proportionality 
when
x=9, y=12,z=15
thus
k=(12*15)/9
k=20
hence:
z=20x/y
thus:
when x=17 and y=16, the value of z will be:
(20×17)/16
=21.25