Answer: Impossible to answer/ 12 chickens 8 rabbits
Step-by-step explanation: The question asks how many hens there are, or female chickens. We do not know if the chickens are female or male, so we cannot answer. If you meant how many chickens there were, then we start with 20 chickens and 0 rabbits. Doing so, we have 40 legs. When we switch a chicken for a rabbit, we have 19 chickens and 1 rabbit, and 42 legs. So, we can subtract 56-40 giving us 16 extra legs we need, so we divide 16/2 giving us 12 chickens and 8 rabbits.