There are 90,000 different number combinations that can be made in a five-digit number if numbers can repeat. To determine the number of possibilities, each place digit has to be evaluated independently to see how many numbers could fit there and then all are multiplied together.
A five-digit number has five different place settings which can take on various values. The first digit can take on nine values, from 1 to 9. For the second through fifth digits any number between 0 and 9 can be used. To find the total number of combinations, these values are then multiplied together: 9 x 10 x 10 x 10 x 10 = 90,000 total combinations.