A Missouri farmer passed away and left 17 mules to his three sons. The instructions left in the will said that the oldest boy was to get one-half, the second oldest one-third, and the youngest one-ninth. The three sons, recognizing the difficulty of dividing 17 mules into these fractions, began to argue.  

Their uncle heard about the argument, hitched up his mule and drove out to settle the matter. He added his mule to the 17,  making 18. The oldest therefore got one-half, or nine, the second oldest got one-third, or six, and the youngest son got one-ninth, or two. Adding up 9, 6 and 2 equals 17. The uncle,  having settled the argument, hitched up his mule and drove home.