《1》(number of rabbit’s feet × total number of chickens – total number of feet) ÷ (number of rabbit’s feet – number of chicken’s feet) = number of chickens;

Total Number of birds - number of chickens = number of rabbits.

We can also assume that they are all chickens, and the formula is:

《2》(Total number of feet - number of chicken feet × total number) ÷ (rabbit’s number Number of feet - number of chicken feet) = number of rabbits;

Total number - number of rabbits = number of chickens.

We can also assume that two of the feet of the chicken and rabbit in the cage are lifted. We can think that only two feet of each rabbit are left in contact with the cage. We get the formula as: total number of feet ÷ 2 - total number of rabbits = number of rabbits; (use multiplication distribution rate)

Total number of legs - number of rabbits = number of chickens.