Try this problem from I.S.I. B.Stat Entrance Objective Problem based on Problem on Digits.
The sum of all the distinct four digit numbers that can be formed using the digits 1, 2, 3, 4, 5 each digit appearing at most once is
Digits
Sum
Non-repeated
Answer: 399960.
B.Stat Objective Problem 111
Challenges and Thrills of Pre-College Mathematics by University Press
here every strings are 1234, 2345, 1345, 1235, 2345
for 1234, sum =66660
for 1235, sum=66+660+6600+66000=73326
for 2345, sum=84+840+8400+84000=93324
for 1345, sum=78+780+7800+78000=86658
for 1245, sum=72+720+7200+72000=79992
then 66660+93324+73326+79992+86658=399960.
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