1. 1 cup from wine bucket A (quantity >= 1 cup) is added to water bucket B (quantity n cups, n>=1):
2. B has n+1 cups mix: n cups water, 1 cup wine.
3. Filling 1 cup from B thus gives a mixture of n/(n+1) cups water and 1/(n+1) cups wine.
4. B, after the cup is taken back, has the original 1 cup of wine, less the amount in the cup going back to A, or 1-[1/(n+1)] cups wine. This simplifies to n/(n+1) as per (3).
5. A, with its n/(n+1) cups water from the mixed cup from B, thus has the same amount of water as there is wine in B.