Find the number of possible choices for a 4-digit (pin) if the digits cannot be repeated find the possible choices of a 4-digit (pin) if the digits cannot be repeated

There are 5040 choices.

There are 10 digits to choose from for the first digit.  Since the digits cannot repeat, there are 9 to choose from for the second; 8 choices for the third; and 7 choices for the fourth.

10(9)(8)(7) = 5040.