Answer: There are 20 pigs and 133 chickens.
Explanation:
We know that a pig has 4 legs and a chicken has 2 legs.
Let x be the number of pigs and y be the number of chickens , then we have the following system of linear equations:-

Multiply 2 on both sides of equation (1), we get

Eliminate equation (3) from equation (2), we get

Put x= 20 in (1), we get

Hence, there are 20 pigs and 133 chickens.