Question

Suppose you must choose a 3 digit code for your locker using the digits 0 through 9 and no digit can be used more than once. How many 3-digit codes are possible?

Answer 1

1st digit can be 0-9 = 10 numbers

2nd digit can be 10-1 numbers = 9 numbers

3rd digit can be 10-2 = 8 numbers

10 x 9 x 8 = 720 codes are possible