There are 14 European cities that Sam would eventually like to visit. On his next vacation, though, he only has time to visit 3
of the cities: one on Monday, one on Tuesday, and one on Wednesday. He is now trying to make a schedule of which city he'll visit on which day. How many different schedules are possible? (Assume that he will not visit a city more than once.)
Sam can make different schedules of the same three cities, so order of cities does matter, but no repetition is allowed. This makes this a permutation without repetition.
When we choose from n items, and we choose r of them, our formula is
n! / (n-r)!. We have 14 things to choose from, and 3 to choose, so our formula becomes
