human
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?
assistant
How many chickens are there? ** 2/3 of the birds are chickens because 1 -(1/3)=2/3
How many chickens are there? ** He has 10 chickens because 15 x (2/3) =<<15*(2/3)=10>>10
How much does it cost to feed the chickens? ** It will cost $20 to feed them because 10 x 2=<<10*2=20>>20
#### 20