Since each number is repeated they will appear equal number of times.
the total numbers that can be formed are 4^4 = 256 numbers..
Of these numbers the units digit will be taken by 1 in (256/4) = 64(Since total numbers are 256 and the digits 1,2,3,4 are four in number).
Similarly the units digit will be taken by 2 in (256/4) = 64
Similarly the units digit will be taken by 3 in (256/4) = 64
Similarly the units digit will be taken by 4 in (256/4) = 64
So the sum of digits in units place is 64(1 + 2 + 3 + 4) = 640
the same way the sum of digits in tens place is 640(1 + 2 + 3 + 4) = 6400
the sum of digits in hundreds place is 6400(1 + 2 + 3 + 4) = 64000
the sum of digits in thousands place is 64000(1 + 2 + 3 + 4) = 640000
The total is 640000 + 64000 + 6400 + 640 = 711040.
