autofill question

I'm having some trouble with the autofill feature. I want to have excel autofill the following formula =sum(J2:J5000)/sum(K2:K5000) such that the rows going down vertically will read:

=sum(J2:J5000)/sum(K2:K5000)
=sum(J3:J5000)/sum(K3:K5000)
=sum(J4:J5000)/sum(K4:K5000)
=sum(J5:J5000)/sum(K5:K5000)
etc. down to
=sum(J4999:J5000)/sum(K4999:K5000)

The problem though is that excel wants to change J5000 and K5000 too, but I want this to remain constant. How do I make this work?

Hi
Does this work,
=sum(J2:J$5000)/sum(K2:K$5000)

http://www.computerhope.com/issues/ch000774.htm