The chief of the tribe sent his braves to scour the world for three beautiful animal skins for each of his three wives to sit on outside his teepee.
One group brought back a beautiful polar bear skin, while another brought back a magnificent tiger skin. The third group was less lucky though and could only return with a smell old hippo skin. Nevertheless, the chief seated each of his wives on a different skin outside his teepee.
His observant teenage son soon noticed though that his dad bedded the wife from the hippo skin far more often than he did the other two and asked his father why. The chief scowled at him and said, "I've told you before that you don't pay enough attention in your maths lessons at school. If you did, you'd know by now that the squaw on the hippopotamus is always equal to the sum of the squaws on the other two hides".
;-)