Question

Let four-digit numbers are 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. $320$
• B. $280$
• C. $120$
• D. None of these

Answer 1

The correct option is C $120$

If we fix the units 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 $6(2+4+6+8)=120$ units.