anagram combination

Question

how many ways can the numbers 1 3 7 and 9 be put like 1379,9137...etc

Answer 1

The answer is n!, where n=4, and 4! = 1 * 2 * 3 * 4.

There are 24 possible permutations.

Think of it this way:

There are 4 choices for the first number.
Then for each possible choice for the first one, there are 3 possibilities for the second number. We now have 3*4 possible results for the first two selections.
There are 2 possibilities for the third choice after each of the 12 combinations of the first two: 2*3*4.
And the last one is then added to the end.
The total number of permutations is 1*2*3*4 = 24