How to become a Multiplication Genius!

By Aditya Mittal

 

Key:

Red: The School Teacher’s method (also known as the Paper/Pencil method)

Blue: The Smart Student’s methods

Maroon: The Experienced Mathematician’s methods

Green: The Genius Puzzle Solver’s methods

 

Contents:

27*6 (Genius not required)

994*998

28232 x 53246 (Geniuses only)

 

 

Teacher’s method of multiplication:

 

27

162

 

This method uses the "carry" and we all learn it in school, so I hope you know how to do this.  In order to use this method, one is not required to understand how multiplication works intrinsically, just how to execute this procedure.

 

Smart student’s method of multiplication:

1. Multiplication by 6 is multiplication by 5 + the number

2. Multiplication by 5 is multiplication by 10 divided by 2

 

27 * 10 = 270

270/2 = ?

 

This method first splits the division into two simpler divisions like 200/2 = 100, 70/2 = 35, and then adds the two results to get 135. (That’s 27*5)

 

135 + 27 = 135 + 20 + 7 = 162

 

The smart student then answers faster than everybody else in math class, while others are still trying to multiply or pulling out their calculators; he might even have done 135 + 27 = 135 + 30 – 3 = 162.

 

The experienced mathematician shows an expertise in the teacher’s method:

:

1.    Knows his tables well.

2.    7 x 6 in the end will be 42 and has this other 120 from the 20*6.

3.    120 + 42 = 162.

 

 

That’s quite simple.  Now who wants to do 998 * 994 without the calculator? 

 

 

Teacher’s method (or the Paper/Pencil method).  I am not going to write this one out but you all better know how to do it.  If you don’t follow the link to http://www.tpub.com/math1/3b.htm and come back later.

 

Smart student’s method:

1.    998 is only 2 away from a thousand.  994* 1000 – 994 – 994 will do it.  Ugh.  Well 994 is 6 away from 1000, so 994*2 should be 12 away from 2000.  so 994k – 2k + 12 = 992,012.

 

The experienced mathematician’s method:

      1: 1000 squared – a = 992,012

 

Where a = (1000-998)*1000 + (1000-994)*1000 – b = 7988

Where b = (1000 – 998)*(1000 – 994) = 12.

 

Genius Puzzle Solver’s method:

 

      1000 – 994 = 6

      1000 – 998 = 2

      998 – 6 = 994 – 2 = 992

      6*2 = 12.  Answer: 992,012.

 

Here is the real puzzle: 28232 x 53246:  How long will this take you? 5 minutes?

                                   

Notice that the method that one uses regardless of the mind's computational speed limits the ease and speed with which the answer is calculated.