Question

The access code for a car’s security system consists of four digits, 0 through 9. Once a digit is used, it cannot be repeated.

There are
choices for the first digit,

choices for the second digit,

choices for the third digit, and

choices for the fourth digit.

Answer 1

There are 10 choices for the first digit, 9 choices for the second digit, 8 choices for the third digit, and 7 choices for the fourth digit. (Total codes = 10×9×8×7 = 5040.)