Four and thirteen
Managed to solve this by hand but I think it was designed to be done by computer
Two integers, m and n, each between 2 and 100 inclusive, have been chosen. The product, mn, is given to mathematician X. The sum, m + n, is given to mathematician Y. Their conversation is as follows:
X: I don't have the foggiest idea what your sum is, Y.
Y: That's no news to me, X. I already knew that you didn't
know.
X: Ahah, NOW I know what your sum must be, Y!
Y: And likewise X, I have surmised your product !!
Find the integers m and n.
I've seen this before. Of course, it's more logic than actual math.
Here's a link to a nice discussion on the matter:
Math Forum - Ask Dr. Math