Question

A lock has a three digit code. how many codes are possible. If a digit can be used only once

Answer 1

below

Explanation:

Let’s assume the first digit can be 0. Then there are 10 choices for each of the 3 digits. 10 * 10 * 10 = 1000 3-digit combinations.

OR

Now, if the first digit cannot be 0, then we have 9*10*10 = 900 possible 3-digit combinations.

Answer 2

720

Explanation:

you have 10 choices for the first digit,you have 9 choices for the second digit and 8 choices for the 3 digit .

It gives you 10×9×8=720 all in all