Suppose that r varies directly with s and inversely with t, and r=2 when s=3 and t=12. What is the value of r when s=5 and t=4?
1 Answer

r = As/t
We have to solve for A first.
rt/s = A
(12 x 2)/3 = 8
Now we can relate the 3 by r = 8s/t
r = (8 x 5)/4
r = 10