Solution of Chicken-Rabbit Cage Equation

There is a famous joke about chickens and rabbits in the same cage:

For example, there are 40 legs in a cage and 15 animals in a cage. How many rabbits and chickens are there?

Answer: Suppose the chickens and rabbits in this cage are well trained. When they whistle, they raise one leg at the same time. At this time there are 40- 15=25 legs in the cage. Blow the whistle again, and they lift one leg at the same time. By this time, the chicken was already sitting on the ground, and only the rabbit had legs in the cage. * * * There are 25- 15= 10, so the number of rabbits is 10%2=5, and chickens are 15-5.