1.

The sum of the digits in the unit place of all numbers formed with the help of 3,4,5,6 taken all at a time isA. 432B. 108C. 36D. 18

Answer» Correct Answer - B
If we fixed 3 at units place.
Total possible number is `3"!"` i.e., 6.
Sum of the digits in unit place of all these numbers `=3"!" xx 3`
Similarly, if we fixed 4, 5 and 6 at units place, in each case total possible numbers are `3"!"`.
Required sum of unit digits of all such numbers `= (3 + 4+ 5 + 6) xx 3"!"`
`= 18 xx 3"!" = 18 xx 6 = 108`


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