Chicken have 2 legs. Rabbits have 4 legs. Let the number of chicken be x and the number of rabbits be y. Then we have the following equations: x + y = 72 (the total number of animals in the cage) and 2x + 4y = 200 (the total number of legs in the cage). In the first equation we express x relative to y and get that x = 72 - y. Then we replace it in the second equation and get 2*(72 - y) + 4y = 200 <=> 144 + 2y = 200 <=> y = 56/2 <=> y = 28. And since x = 72 - y we get that x = 44. So in total we have 44 chicken and 28 rabbits.
