A woman owns 21 pets.

Question

A woman owns 21 pets. Each of her pets is either a cat or a bird. If the pets have a total of 76 legs, and assuming that none of the birds legs are protruding from any of the cats' jaws. how many birds does the woman own.

Answer 1

Start with what you know:
21 = number of pets
76 = number of legs
x= number of birds
cats have 4 legs each
birds have 2 legs each
21 – x = number of cats

number of legs/cat * number of cats + number of legs/bird * number of birds = number of legs
Thus:
4(21-x) + 2x = 76

Solve for x:
84 – 4x + 2x = 76
84 -2x =76
8 = 2x
x = 4
4 birds