Question

How many 5 digit zip codes are possible? Zero can be a digit.

Answer 1

There are ten possible digits (0 to 9).

If they can be repeated, you're looking at 10 * 10 *10 * 10 * 10, or 105

This means 100000 possible zip codes if repeatable.

If not, you're looking at one less each time:

10 * 9 * 8 * 7 * 6

90 * 56 * 6

540 * 56 = 30240 zip codes without any repetitions.