2nd Step to Becoming Human Calculator (Multiplication)

Hi folks…. Hope you are guys and gals are number healthy. In this post we will be looking into fun and easy way to multiply. We will start of with 2 digits multiplication today and move on to 3 digits in later post.  At the end of this, you should be able to say how easy this could be and with a little practice you will be on track to be the next ‘HUMAN CALCULATOR’.

Let’s look into the problem stated below. What would be our usually method of approaching this problem? Well they way it was thought in school were multiply 3x4 which results in 12. Write 2 in the one’s column and bring 1 to the ten’s column.  Next multiply the 1x4 and add the 1 (which was carried forward earlier). This gives us a total value of 5. Then we repeat the same problem for 2. We multiply 2x3 which is equal to 6 and place it as shown below and next we multiply 1x2. And the final result will be 312.

                 13                      13                        13                 

            x    24              x      24                 x     24 

                 52                      52                        52

                                         26                        26

                                                                    312  

Well, this conventional method is not wrong. It is just not user friendly when we want to do mental arithmetic. For us to become human calculator we need to think of a simplified solution to multiply. Scott has shown a simplified version to this. We still approach this from right to left (unlike addition).

Multiply 3x4 (=12). Write the 2 in the one’s column and carry forward the 1. Next cross multiply (1x4) + (2x3). This will sum up to be 10. Add the 1 that was carried forward earlier and the sum now becomes 11. Thus write the 1 as shown below and carry forward the 1 similar as earlier to the tens column. Finally, just multiply 1x2 and add the carry forward value earlier. Thus, this will be 2 + 1 = 3. In which it gives us the final answer 312. Now with a little practice (similar like previous), you will be able to master this technique and could perform and 2 digits multiplications mentally without hassle.

               ¹13                    ¹13                      ¹13                 

            x   24              x      24                 x     24 

                   2                     12                      312

Below are some questions for you to play with…

                 16                      24                        63                 

            x   24              x       42                 x     21 

                 84                      42                        85                 

            x   93              x       21                 x     27 

Till we meet again in our next post, have fun and be number healthy folks….