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? Let's answer step by step:
2 / 3 of the birds are chickens because 1 - (1 / 3) = 2 / 3. He has 10 chickens because 15 x (2 / 3) = 10. It will cost $20 to feed them because 10 x 2 = 20. The answer: 20.