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Mathstud28 · #10 April 20th, 2008, 08:14 AM

Quote:

Originally Posted by Moo

Hello,

1.*1.

This has nothing to do with extraordinary technique, but you gotta think about it (I'm confident that some of you know about it)..

$(10+a)(10+b)=10(10+a)+b(10+a)=10(10+a)+10b+ab=10(10+a+b)+ab$

So multiplying two such numbers is equivalent to :

- sum one of the numbers with the unit digit of the other one
- multiply it by 10
- add the product of the two unit digits.

$19 \times 17= ?$

- $17+9=26$

- $26 \times 10=260$

- $7 \times 9=63$

- $19 \times 17=260+63=323$

I hope this would help at least one person in the future

Enjoy calculations !

Hi Moo,

I was jus wondering if you do this....say I solve an equation and get $x=\frac{288}{128}$ ...my mind works like this $x=\frac{200+88}{100+28}=\frac{4(50+22)}{4(25+7)}=\frac{77}{37}$ that is how my mind simplifies things...its much quicker in my mind though...is that how you process things?