Farmer Brown has 20 animals on his farm, all either chickens or cows. They have a total of 70 legs, all together. How many of the animals are chickens?
Let C be the number of chickens.
There are 20-C cows.
The cows have 4*(20-C) legs.
The cows have 2C legs.
The total number of legs is 2C+4(20-C)=70.
2C+80-4C=70
2C=10
C=<<5=5>>5
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