permute and sum

in how many ways we can make a 4 digit no. using 1,2,3,4 and what's the sum of all the numbers obtained?(repeatations not allowed)

2 Answers

Himanshu Giria ·


Manish Shankar ·

There will be 24 numbers.

out of these 24, 6 will have 1 in unit digit, 6 will have 2 in unit digit, 6 will have 3 in unit digit and 6 will have 4 in unit digit.

Similar things can be said about the other digits.

Sum of number at unit digit=6*(1+2+3+4)=24
Sum of number at tens digit=6*(1+2+3+4)=24\
Their contribution to the sum will be 24*10=240

Similarly at hundredth digit sum is 24*100

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