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Easy Graphical Multiplication Trick

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Easy Graphical Multiplication Trick E-mail
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It's not a way to make mental multiplications easier, it's just a funny way to resolve graphically a multiplication. It's only meant to be a little trick to show to friends and kids who hate maths. It's NOT meant to be efficient as some seems to think. You can do any kind of multiplication with it but yes it's boring to draw numbers like 8 or 9.

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Explanation
21•13 = (20 1) (10 3)
= (2•[10] 1•[1]) (1•[10] 3•[1])
= (2•1)[10•10] (2•3 1•1)[10•1] (1•3)[1•1]
= 2•[100] (6 1)•[10] 3•[1]
= 2•[100] 7•[10] 3•[1]
= 273
In this case, for each number the first drawn lines represent 'tens', and the others represent 'units'. That is:
21 --> 2 'tens' lines (10 10)
13 --> 1 'tens' line (10) and 3 'units' line (1 1 1)
Intersecting: (2 'tens' lines x 1 'tens' line) = 2 'hundreds' intersection points = 200
[That is: 20*10 = 200]
Intersecting: (2 'tens' lines x 3 'units' lines) (1 'units' line x 1 'tens' line) = 7 'tens' intersection points = 70
[That is: 20*3 1*10 = 60 10 = 70]
Intersecting: (1 'units' line x 3 'units' lines) = 3 'units' intersection points = 3
[That is: 1*3 = 3]
TOTAL: 273
Similar for the second example.



Another graphical multiplication trick

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