Question

A zip code contains 3 digits. How many different zip codes can be made with the digits 0–9 if no digit is used more than once and the first digit is not 0?

Answer 1

For the first position, there are 9 possible choices (since 0 is not allowed). After that number is chosen, there are 9 possible choices (since 0 is now allowed). Then, there are 8 possible choices.
9 × 9 × 8 = 648