MATHS SHORT CUTS

MULTIPLICATION

Question: Multiply 432 by 617.
Answer:
       432
    x 617     3024
     432
 2592   
 266544

More the number of digits in the numbers, more lines and time you consume.
Step 1 (mentally, don't write on notebook) : vertically (last digits) :
          2x7=14; write 4 carry 1
Step 2 (mentally) : crosswise (last two digits) :
          3x7 +2x1 = 23 +carry 1 = 24; write 4 carry 2
Step 3 : vertically and crosswise (three digits) :
           4x7 + 3x1 +2x6 = 43 +carry 2 = 45; write 5 carry 4
Step 4 : (move left; first two digits) :
             4x1 +3x6 = 22 +carry 4 = 26; write 6 carry 2
Step 5 : (move left; first digit of each number) :
             4x6 = 24 +carry 2 = 26. End.
Write answer : 266544
This is how it appears on notebook :
        432
     x 617
  266544

No matter how big the numbers are, you will need to write only the final answer. All other steps are easily carried out mentally. If the two numbers have different number of digits, write smaller number below the other and pad it on left side with zeros. 


Multiply 92 by 67
    92
 x 67
(Mentally) 2x7 is 14; write 4 carry 1;
9x7 +2x6 = 75 +carry 1 = 76; write 6, carry 7
9x6 is 54, add carry 7 to get 61 -so answer is 6164

Multiply 2376 by 4060
     2376
 x 4060
6x0 = 0; write 0;
7x0 +6x6 = 36; write 6 carry 3;
3x0 +7x6 +6x0 = 42 +carry 3 = 45; write 5 carry 4
2x0 +3x6 +7x0 +6x4 = 42 +carry 4 = 46; write 6 carry 4
2x6 +3x0 +7x4 = 40 +carry 4 = 44; write 4 carry 4
2x0 +3x4 = 12 +carry 4 = 16; write 6 carry 1
2x4 = 8 +carry 1 = 9; write 9. End. Answer is 9646560

Note that all the calculations can be easily done in mind; you just go on writing a digit of answer one at a time (from right to left). So on notebook you will just write:
     2376
 x 4060
9646560