If z varies jointly with x and the square of y, and z=600 when x=2 and y=5, find the positive value of y when z= 4608.

Question

If z varies jointly with x and the square of y, and  z=600 when x=2 and y=5, find the positive value of y when z= 4608.

jamesj · Answer

"z varies jointly with x and the square of y"
means
z = Cxy^2 for some C.

Now use z=600 when x=2 and y=5 to find C

anonymous · Answer

I already got C to equal 60, and when I solve for y I get the $$\sqrt{12.8}$$, which not one of the answer choices.  The answer choices are 4, 6, 8, and 10.

jamesj · Answer

That's the wrong value for C

anonymous · Answer

600=50C thus C=12 and we have z=12xy^2

anonymous · Answer

Are we still assuming x=2 in solving for y when z=4608?

anonymous · Answer

Oh, I see.  I wasn't sure if I had to square y or not.
Thank you.