To use an automated teller machine (ATM), a customer must enter his or her four-digit Personal Identification Number (PIN). How many different PINs are possible?

10000 possible PINs.

Explanation:

Considering the fact that only numbers are permitted (0 - 9) which gives 10 characters and also that the digits can be repeated, the total number of possible PINs that are possible is 10 x 10 x 10 x 10 = 10000