Question

How many 6 digit numbers can be form from 1 2 3 4 5 6 7?

Answer 1

We know,
$n_{c_r} = \frac{n!}{r!(n - r)!}$
$7_{c_6} = \frac{7!}{6!(7 - 6)!}$
$= \frac{5040}{720} \\ = 7$
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