Q) the sum of 4 digit numbers formed by 1,2,4 &6 is?
Sol) The total no. of 4 digit numbers formed by 1,2,4 & 6 is 4!
i.e 24 combinations are possible. All digits occur 6 times at all places
Thus sum of digits at each place is (1+2+4+6) x 6 = 78
Thus sum of all digits at units place = 78
(Thus digit at ones place = 8)
Sum of all digits at tens place = 78 + 7 = 85
(Thus digit at tens place = 5)
Sum of all digits at Hundred's place = 78 + 8 = 86
(Thus digit at Hundred's place = 6)
Sum of all digits at Thousand's place = 78+8 = 86
Thus the sum is = 86658