If all the six digit numbers x 1 x 2 x 3 x 4 x 5 x 6 with 0 < x 1 < x 2 < x 3 < x 4 < x 5 < x 6 are arranged in the increasing order, then the sum of the digits in the 72 th number is _______.

Step-by-step solution

Taking case 1 fixing 1   &   2 at first two places, 1 2 So, other number can be selected in C 4 7 = 35 ways as number are from 1-9 Case 2 fixing 1   &   3 at first two place, 1 3 So, other number can be selected in C 4 6 = 15 ways Similarly, 1 4 So, other number can be selected in C 4 5 = 5 ways Now fixing 1   &   5 we get, 1 5 Other number can be selected in C 4 4 = 1 Now fixing 2   &   3 in first two place, 2 3 So, other number can be sel