Each son needs ten flasks and five flasks’ worth of oil. The neat split gives two sons 5 full and 5 empty each, and the third all 10 half-full. Any split works as long as each son has as many full flasks as empty ones and the half-full ones make up his ten.
A man dies and leaves his three sons 30 flasks of oil. Ten are full, ten are half full and ten are empty. How do they split them so each son gets the same number of flasks and the same amount of oil, without pouring a drop from one flask into another?
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Two half-full flasks hold as much oil as one full one.
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Each son takes as many full flasks as empty ones
Source: Alcuin of York, Propositiones ad Acuendos Juvenes, No. 12, c. 800