2/3 of the birds are chickens because 1 -(1/3)=2/3

He has 10 chickens because 15 x (2/3) =<<15*(2/3)=10>>10

It will cost $20 to feed them because 10 x 2=<<10*2=20>>20

# Answer

20
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Peter has 15 birds. 1/3 are ducks. The rest are chickens and require special feed that costs $2 per bird. How much does it cost to feed the chickens?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
20
Peter has 15 birds. 1/3 are ducks. The rest are chickens and require special feed that costs $2 per bird. How much does it cost to feed the chickens?
train