Question

area codes are made up of three digit numbers
a. if all numbers can be used for each digit, how many area codes are possible
b. how many area codes would be possible if repetition is not allowed?

Answer 1

Any guesses for a) ?

Answer 2

10*100 is 1000 I think

Answer 3

Why 10*100?

There is 1000 though, but there's a better way to get it than 10*100