Elementary combinatorics: Factorial and binomial coefficient
Factorial
You use \(4\) different digits from \(\{1,\ldots, 9\}\) and make a number with it.
For example, with \(1, 4, 5, 7\) you can form the number \(7541\).
How many different numbers can you write down with the given \(4\) digits
| amount of numbers that can be written down = |
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