Tuesday, April 24, 2012

Easy way to memorize multiplication
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I introduced this method to my students, but it seem like not working! They still using their traditional method to find the answer.  For example, 2 x 8 = 2 + 2 + 2 + 2 + 2  + 2 + 2 + 2 = 16. Sadly, why they don't just add number 8 twice?! 2 x 8 = 8 x 2 = 8 + 8 = 16. Simple. They can't think of it. I don't blame them (I swear!).

I think 80% of math teachers knew this method. I will just share it again.

Multiplication of number 3 and 7

1.  Arrange the number as below:

         1         2          3
         4         5          6
         7         8          9

Multiplication of number 3:
                                                         start here     
                                                             \/
       2  1   <= 3x7     1     <= 3x4        3     <= 3x1
       2    <= 3x8     1     <= 3x5        6     <= 3x2
         <= 3x9     1  8    <= 3x6        9     <= 3x3

Multiplication of number 7:
                                                       
       2  1   <= 7x3     4      <=7x6      6   3     <= 7x9
       1    <= 7x2     3     <= 7x5      5   6     <= 7x8
             <= 7x1     2  8    <= 7x4      4   9     <= 7x7
           /\
     start here

Multiplication of number 9 (you can use your fingers too)

  Arrange number as below:
                    8    1        <= 9x9
                    7    2        <= 9x8
                    6    3        <= 9x7
                    5    4        <= 9x6
                    4    5        <= 9x5
                    3    6        <= 9x4
                    2    7        <= 9x3
                    1    8        <= 9x2
                          9        <= 9x1
                          /\

                     start here
 
To be continued..