If there were a 4 digit number using any combination of the numbers 0-9, HOW MANY POSSIBLE COMBINATIONS WOULD THERE BE? For example the last four digits of the social security numbers, how many numbers are possible there and how do you compute it? I had several ideas but thought surely someone knows exactly how to do this correctly…what better place then here to ask?
10,000…the numbers from 0 to 9,999.
According to this page, there are 10,000 combinations. Reasoning given.
10 possibilities for each digit, four digits total, gives you 101010*10 or 10[sup]4[/sup] or 10,000.
And, for completeness, if your combos also include letters, the number of possibilities is 363636*36, or 36^4, or just short of 1.7 million.
The “why” is 10 numbers (0-9) plus 26 letters (a-z).
If you allow mixed case, the choices become 0-9 plus a-z plus A-Z, (10+26+26) – 62^4 = just under 14.8 million combinations.
10,000 makes sense…I thought so but had another person tell me that was not correct. Thanks 
One could argue that the answer is 9999, but that’s if you forget (or exclude) 0.
Although the person making that argument doesn’t really have a leg to stand on…