Level of question: middle 6-9
Question: A farmer has 21 pigs and 4 pens, he must put an odd number of pigs in each pen, how does he do it?
He doesn't. The sum of two odd numbers is an even number and hence the sum of four odd numbers is an even number. Thus if you have an odd number of pigs in each of the four pens then, in total, you have an even number of pigs.Penny
Chris disagrees with Penny. He says "I suppose that he could have some pens inside others."