Thread: Mental calculus tips..
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Old April 18th, 2008, 01:58 PM
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Hello

I didn't know about this hint. Usually, I simply develop (10+a)(10+b)=100+10(a+b)+ab.

In the case of 19 \times 17, where 9 and 7 are close to 10, I'd rather do 19\times17=(20-1)(20-3)=400-20(1+3)+3 which avoids manipulating too large numbers. (yes, I consider 63 as large )
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