First slide
Permutations
Question

The number of 9 digit numbers which have all distinct digits, is

Moderate
Solution

The required number of ways

= The number of ways of permuting nine digits out of ten digits 0, 1, 2, …, 9

– The number of ways of permuting nine digits out of nine digits 1, 2, …, 9

=10P99P9=10!1!9!=10!9!

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