Question

how can we solve permutation question

Answer 1

Each of the arrangement which can be made by taking some or all of a number of thing is called a permutation
n number of things can be selected in n! ways
then
$P_{r}^n$ is Number of permuatations of n different things taken r at a time
$P_{r}^n= \frac{n!}{(n-r)!}=n(n-1)(n-2) ....(n-r+1)$
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