Numbers - General Aptitude

Q1:

What least number must be subtracted from 13601, so that the remainder is divisible by 87 ?

A 23

B 31

C 29

D 37

E 49

ANS:C - 29

 87) 13601 (156
     87
     ----
      490
      435
      ----
       551
       522
       ---
        29
       ---
       
 Therefore, the required number = 29.