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) !
```

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