A hot dog consists of a sausage in a bun with sauce. Onion, tomato, pineapple and cheese are available as extras. How many different types of hot dog can be made?
Using only one extra you get 4 different hot dogs.
Using two extras you get 4C2 = 6 different hot dogs.
Continue in this way and then add them all up.
I assume a hot dog with no extras counts as a seperate type ....?