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Sum of unit digit of all the number formed by given n different digit

Given : n different digit
i.e a1 , a2 , a3 .....................................an

Total Number having unit digit an = (n-1) !

Sum of unit digit of all the number having unit digit an = an (n - 1) !

Sum of unit digit of all the number formed =

  =   a1 (n -  1) !  +  a2(n  - 1) !      +    ...    +   an  (n  -1 ) !

  =     (a1   +   a2   +  .......    +   an )  (n  -  1) !

  =  (Sum   of   digits) (n  -1) !

Note by Vibha Sharma
1 year, 9 months ago

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