Systems of linear equations

Question

 There are 64 animals on Mrs. Ercoli's farm. The animals have a total of 168 legs. How many 4-legged animals and 2-legged animals are there?

Answer 1

a + b = 64 ------> a = 64 - b

4a + 2b = 168

 

Substitute!

 

4(64 - b) + 2b = 168

256 - 4b + 2b = 168

2b = 88

b = 44

 

a = 64 - 44 = 20

 

There are 20 four-legged animals and 44 two-legged animals.