India's 9-9 multiplication-super strong

9-9 multiplication in India
The ninth multiplication table in India is from 1 Back 19 ( → 19th multiplication? ) ,
But you know how Indians remember 11 To 19 Number of words?
I suddenly realized it after reading this article.
「 Indian computation example 」
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This section describes various fast computing methods for multiplication and division, but here I only describe the 9-9 multiplication of India.
It's amazing !!
The following data and description all reference P.44 .
Please calculate the following answer with your mind:
13x12 = ?
( Multiplication number )( Multiplication )
This is the case for Indians.
This is the case for Indians.
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Step 1:
Multiply the number first (13) The number of digits that follow the multiplication. (2) Add
13 + 2 = 15   Step 2:
Then the number of multiplied digits (3) Multiply by the number of digits (2)
2x3 = 6

  Step 3:
Then multiply the answer of the first step 10 ( → That is, add 0) Add the answer in step 2.
15x10 + 6 = 156
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In this way, you can quickly calculate with your mind. 11x11 To 19x19 Oh.
This is amazing!
Let's continue to calculate
14*13 :
(1) 14 + 3 = 17
(2) 17*10 = 170
(3) 4*3 = 12
(4) 170 + 12 = 182