How many different ways can you write 1 2 3 4?

Answer 1

I guess you mean how many ways can the 4 digits 1, 2, 3, 4 can be written, that is "1 2 3 4", "1 2 4 3", etc

There are 4 choices for the first digit, with 3 choices left for the second digit for each of these, 2 for the third and 1 for the fourth (and last) digit, that is:

4 x 3 x 2 x 1 = 24 ways.