[M.D. Holloway]

There is no tricky part in this question. The two cups are identical. The same spoon is used in both transfers. There is nothing funny to catch. It doesn't even matter whether you stir up the cups after each move or not. You can stir up thoroughly, stir up a little, or do nothing to stir up, after each move. You can heat the two cups up, cool them down, or heat one up and cool the other down. You can do these two moves once, twice, or until you get nauseated. They all come out the same answer!

(I found this on-line)