text: Do you mean just the numbers 1-9?  Or do you mean all the digits, including 0, which would be 10 digits?\n\nIf you mean 10 digits 0-9 and assuming that numbers such as 0000 are valid, then you have 10^4 = 10,000 possibilities (0000, 0001, 0002, ...., 9997, 9998, 9999 -- count 'em up, there are 10,0000).\n\nIf you really mean just nine digits, then you have 9^4 = 6,561 possibilities (you have 9 choices for your 1st digit, nine choices for your 2nd digit, 9 choices for your 3rd digit, and 9 choices for your 4th digit = 9*9*9*9 = 6,561).\n\nYou didn't say that once you use a digit it cannot be repeated.  If you meant this, then the folks who are saying the answer is 9*8*7*6 = 3,024 are correct.\n\n~ ♥ ~