We’re going to see how far we can get in implementing a supermarket checkout that calculates the total price of a number of items. In our store, we sell Apples, Bananas, Carrots and Drinks. Our goods are priced individually. In addition, some items are multi priced: buy n of them, and they’ll cost you x pounds. For example, an Apple might cost 50 pounds individually, but this week we have a special offer: buy three Apples and they’ll cost you 130. The price and offer table:

Item    Price   Offer
--------------------------
Apple   50      3 for 130
Banana  30      2 for 45
Carrot  20
Drink   15