COMPUTER KNOWS ADDITION ONLY!

 

  

 We know there are four fundamental operations namely addition, subtraction, multiplication, and division.  Multiplication is the repeated addition and division is the repeated subtraction.  So we are left with only two fundamental operations addition and subtraction.  But subtraction can be done in terms of addition as follows. 

To subtract 6 from 9. get the 10's compliment of 6, which is 10-6 = 4. add the 9 and the compliment    9+4 = 13. then drop the carry 13 = 3 which is the answer.    So we require only addition. 

     In computers, all numbers are represented in binary. That is, in 0's and  1's .  So 1's compliment is 0 and 0's compliment is 1.  Hence computer does the subtraction in terms of addition easily.  
     Computer does all the mathematical operations using addition only.  It is easy for computers not for humans.