math word equation

Question

A farmer saw some chickens and pigs in a field. He counted  heads and  legs. Determine exactly how many chickens and pigs he saw.

Answer 1

c = number of chickens with 2 legs and 1 head

p = number of pigs with 4 legs and 1 head

2c + 4p = 86 (number of legs)

c + p = 30 (number of heads)

Now solve this system of 2 linear equations in 2 unknowns c and p. From the bottom equation, get c = 30-p. Plug that into the top equation and solve for p. Then plug the result for p into either equation and solve for c.