A wealthy Arab owned a stable of seventeen horses. When he died he bequeathed the horses to his three sons.
The will stated that eldest son was to be given one half of the horses, the middle son was to be given one third of the horses, and the youngest son was to be given one ninth of the horses.
The sons were distraught. It was clear to all that the horses could not divided in this way without making a bloody mess, so they decided to call upon a wise, old friend.
The wise man brought with him another horses, which he added to those in the stable, making a new sum of eighteen horses.
In accordance with the Arab's will, he then gave the eldest son half of them (9 horses), the middle son a third (6 horses) and the youngest son one ninth (2 horses). This made a sum total of seventeen horses, which meant that one horse was left over for the wise man to take back home.