Permutations and Combinations
The sum of all four-digit numbers that can be formed by using the digits (when repetition of digits is not allowed) is
- None of these
Correct Answer: Option(a)
Solution: Total numbers ending with is as after fixing in the unit's place other three places can be filled by ways.
Thus, appears in the unit's place times.
Similarly, all other digits and also appear times.
Then sum of the digits in the unit's place is .
Similarly, sum of digits in ten's place is tens and that in hundred's place is hundreds, etc.
Hence, sum of all the numbers is .