Question

How many four-digit key combinations are there if no digits are to be repeated?

Answer 1

If zero is included, there are 10 digits to select from. The number of permutations of 10 digits taken 4 at a time is:
\[\large 10P4 = \frac{10!}{(10-4)!}=you\ can\ calculate\]

Answer 2

The right hand side of the equation can be simplified to:
\[\large \frac{10!}{6!}\]

Answer 3

@annatchernyak Are you there?

Answer 4

@kropot72 Thank you so much ! yes its 5040

Answer 5

You're welcome :)