How many different 4-digit numbers can be formed using only digits 1, 2, 3, and 4, given that they contain each of these digits only once?

24.

Step-by-step explanation:

To solve this question, you might need to do a little math. So, there are four digits, correct? And they cannot be repeated? Well, you can solve this problem by creating the numbers. Here are the ones I came up with:

1234

1324

1432

1342

1243

1423

See? There are 6. You can do the same with these:

2341

2413

2314

2143

2134

2134

These are only half of the expressions. Hopefully this helps you come up with the rest. Best of luck.

9x