Problem on Permutation (Interesting One)

Using the digits 1,5,2,8 four digit numbers are formed and the sum of all possible such numbers?

Answer

24 numbers can be formed. 1528 1582 1258 1285 1825 1852 2158 2185 2581 2518 2851 2815 5128 5182 5218 5281 5812 5821 8152 8125 8512 8521 8215 8251.

each number comes 6 times in unit 10's 100's and 1000th places.

The sum is 106656

1*6+5*6+2*6+8*6 96

96+96(10)+96(100)+96(1000) 106656