Eric owns eleven animals. some of his animals are rabbits and some are chicken. if there are a total of 38 legs what is the number of chickens does eric have

He would have 3 chickens

Total Animals = 11
Total legs = 38

Assumed all the animals are chicken:
11 x 2 = 22 legs

Difference in legs:
38 - 22 = 16

The difference in legs between rabbits and chicken:
4 - 2 = 2 

Number of rabbits = 16 ÷ 2 = 8

Number of chicken = 11 - 8 = 3

There are 8 rabbits and 3 chickens.

Check: 
(8 x 4) + (3 x 2) = 38 legs

The variables should add up to equal 1

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