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Question

Let four-digit numbers be formed by using the digits 2,4,6,8 (when repetition of digits is not allowed). Then sum of unit digits of all the numbers is

A
320
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B
None of these
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C
120
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D
280
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Solution

The correct option is C 120
If we fix the unit's place with 2, then 3! numbers can be formed with given digits.
Hence, total numbers ending with 2 is 3!.
Similarly, all other digits 4,6 and 8 also appear 3! times.
Therefore, sum of the digits in the unit's place is 6(2+4+6+8)=120

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