FInd the number of 4-digit numbers, where each digit is 0, 1, or 3.
I will assume there cannot be a 0 in the first position
2 choices for first digit
3 choices for 2nd
3 choices for 3rd
3 choices for 4th
2 x 3 x 3 x 3 =....... choices
For each digit space, there can be any number, with the exception that the 1000s place cannot have a 0. We have 2 choices for the thousands place, either 1 or 3.
For the 100s place, any number is okay. 0,1, and 3 all work just fine
For the 10s place, any number can be there as well
For the 1s place, it's still 3 choices
So we have 2 choices, 3, choices, 3 choices, and 3 choices. What now? Well, we multiply our answers together, just how you would do a "clothes combination" problem. I will let you do the multiplication for yourself.