Logic v Algebra

100 Animals for £100

A long time ago, before the age of credit cards when cash was king, a farmer sends his Lad to market to buy some Chickens, Pigs and Cows. He gives his Lad £100 and says he wants every penny spent on the required animals. He also tells the Lad that he wants him to buy exactly 100 animals and at least one of each.

When the Lad gets to market, Chickens are 2 for a £1, Pigs are £3 each and Cows are £10 each.

How many of each animal did the Lad buy, to satisfy the farmer’s requirements?