The monkey had a tough time. To make it up to him, I want to give him a cup of banana juice.
I have a big vat of the stuff (don’t ask), but can only give him exactly 4 fluid ounces (any less and he gets angry, any more and he dies).
However, the really bad news is that I have a cup that will contain 5 fluid ounces when full and another one that contains 3 fluid ounces when full.
How can I use the two cups to measure exactly 4 fluid ounces and so keep the monkey happy?