A rabbit has four legs, a chicken has two legs, and the relationship between a rabbit and a chicken is 4-2=2. Rabbits have two more legs than chickens, and chickens and rabbits have 50 legs. If the number of chickens and rabbits is exchanged, the number of legs becomes 52, 52-50=2, which proves that after the exchange, one rabbit increases and one chicken decreases. 50+52= 102 is the sum of rabbits and chickens with 4+2=6 feet, so the number of rabbits and chickens is 102÷6= 17. Because there are more chickens than rabbits 1, there are 9 chickens and 8 rabbits.