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Question
The total number of 9 digit numbers which have all different digits is ______.
Options
10!
9!
9 × 9!
10 × 10!
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Solution
The total number of 9 digit numbers which have all different digits is 9 × 9!.
Explanation:
We have to form 9 digit numbers from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
And we know that 0 cannot be put on extremely left place.
So, first place from the left can be filled in 9 ways.
Now repetition is not allowed.
So, the remaining 8 places can be filled in 9!
∴ So, the remaining 8 places can be filled in 9 × 9!
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