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#1 2011-05-04 21:45:06
- 123ronnie321
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Cool way to square multiples of five
Think of any number that is a multiple of five.
Eg. - 65.
65 is between 60 and 70. So multiply them in your mind 60×70=4200. Attach 25 in the end.
∴65²= 4225.
Can you guess why it works?
#2 2011-05-04 22:09:13
- bobbym
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Re: Cool way to square multiples of five
Hi 123ronnie321;
If a is the number you want to square and it ends in 5 then adding 5 and subtracting 5 will produce ( a + 5 ) ( a - 5).
So a^2 = ( a + 5 ) ( a - 5).= a^2 - 25
The only way to make this equation true is to add 25 to the RHS,
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#4 2011-05-04 22:13:13
- bobbym
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Re: Cool way to square multiples of five
Hi;
How are you doing with the Vilenkin book?
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.
#5 2011-05-04 22:22:04
- 123ronnie321
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Re: Cool way to square multiples of five
I read the first few pages and found it interesting. The author has given some nice practical examples about where this field is used.
I have no idea about computers but he has given some nice information on "small" computer 'Strela'. 
#6 2011-05-05 01:46:31
- bobbym
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Re: Cool way to square multiples of five
Hi 123ronnie321;
Good! Combinatorics is a fun part of math. It is growing rapidly into one of the most important parts of math.
In mathematics, you don't understand things. You just get used to them.
Probability is the most important concept in modern science, especially as nobody has the slightest notion what it means.
90% of mathematicians do not understand 90% of currently published mathematics.