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Q.
The sum of all the five digit numbers formed with the digits $1, 2, 3, 4, 5$ taken all at a time, is
Permutations and Combinations
Solution:
Sum of unit's place $= 4!(1 + 2 + 3 + 4 + 5)$
$ = 24 \times 15 = 360$
[Since $1$ will come $24$ times in unit place and so the other digits if $5$ digit number is formed with digits $1, 2, 3, 4, 5 $ taken all at a time]
So the sum in tens, hundreds, thousands and ten thousands places is $= 360 \times 10000 + 360 \times 1000 + 360 \times 100 + 360 \times 10 + 360$
$ = 3999960$.