Question

To access his bank’s ATM, Tom must choose a four-digit PIN. Any digit from 0 through 9 can be used in the PIN, but digits may not be repeated. How many possible PIN numbers are there?

Answer 1

Answer:

5040

Explanation:

Answer 2

The first digit can be any one of the 10 available digits.
. . . For each one . . .
The second digit can be any one of the 9 unused others.
. . . For each one . . .
The third digit can be any one of the 8 unused others.
. . . For each one . . .
The fourth digit can be any one of the 7 unused other.

So the total number of possible choices is

(10 x 9 x 8 x 7) = 5,040 possible PINs