The chicken and the rabbit are in the same cage.

Solution 1: (rabbit foot number × total foot number-total foot number) ÷ (rabbit foot number-chicken foot number)

= Number of chickens

Total number-number of chickens = number of rabbits

Solution 2: (total number of feet-chicken feet × total number of feet) ÷ (rabbit feet-chicken feet)

= the number of rabbits

Total-number of rabbits = number of chickens

Solution 3: total number of feet ÷2- total number of heads = number of rabbits.

Total number of rabbits = number of chickens.