Question

What is the formula to get 4 digit combinations from numbers 0-9?

Answer 1

Please read the explanation, because the answer is either `10,000` or `5,040`.

Explanation:

Since there are `10` choices for each digit, the number of `4`- digit combinations is given by
`10*10*10*10 = 10,000`,

UNLESS using a digit means it cannot be used again. In that case, the number of `4`-digit combinations is given by
`10*9*8*7 = 5,040`.