A farm has chickens and cows. You ask the farmer how many chickens he has, and how many cows he has. The farmer tells you he has 28 healthy animals, and they have a total of 64 legs. How many of his animals are cows.

Well, we know that cows have four legs, and chickens have two. See how many times two goes onto 64, and how many times four goes into 64. 64 divided by two is 32. There are 32 chickens. 64 divided by four is 16. There are 16 cows.