Here is a curious little problem. A man had a ten-gallon keg full of
wine and a jug. One day he drew off a jugful of wine and filled up the
keg with water. Later on, when the wine and water had got thoroughly
mixed, he drew off another jugful and again filled up the keg with
water. It was then found that the keg contained equal proportions of
wine and water. Can you find from these facts the capacity of the jug?