Question

A combination lock is to have 4 digits (using the numbers from 1 to 9 (ie No Zero)How many different combinations are there that have all different numbers.

Answer 1

3024

Explanation:

You have to think of this in choices. You have 9 choices for the first lock (because there are 9 numbers). We would have 9 choices for the second lock, but we used one number for the previous one. So we would have 8 choices. We would continue with 7 choices for the third lock and 6 for the fourth.

Multiplying this we get 9x8x7x6=3024