CAT Exam Model Paper 6 with solutions for free online practice

The maximum possible remainder must be less than 18 as the sum of any two digits can not be greater than 18. So we check when the sum of digits is 18.
If the sum of digits is 18 the only possible remainder is 9 in case of 99. Similarly if the sum of digits is 17 the maximum possible remainder is 14 in case of 98. Similarly if the sum of digits is 16 the maximum possible remainder is 15 in case of 79. The remainder we have already got is 15 and all other sums of digits will be 15 or less than15. So 15 has to be the answer.