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The sum of the even numbers

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by cramya » Tue Dec 23, 2008 8:25 pm
I think the formula fo sum of even numbers from 1 to n is

(n-1) / 2 * (n+1) / 2

(n-1) / 2 * (n+1) / 2 = 79 * 80

(n-1) (n+1) = 2*79 * 2*80
= 158 * 160

n=159
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by parallel_chase » Tue Dec 23, 2008 8:29 pm
cramya wrote:I think the formula fo sum of even numbers from 1 to n is

(n-1) / 2 * (n+1) / 2

(n-1) / 2 * (n+1) / 2 = 79 * 80

(n-1) (n+1) = 2*79 * 2*80
= 158 * 160

n=159
Nice work cramya, I wasnt aware of such formula. Thanks.
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by amitabhprasad » Tue Dec 23, 2008 10:41 pm
Thanks cramaya, I was not at all aware of this formula. Howmany more you have up your sleeve :)
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by cramya » Tue Dec 23, 2008 10:45 pm
Amit,

Check this out:

https://www.beatthegmat.com/help-questio ... tml#108282

Hate to take away someone's bubble,so sharing the link for other formulas.. I havent tested it out myself (to convince myself) but feel free to.

Regards,
Cramya
Last edited by cramya on Tue Dec 23, 2008 10:56 pm, edited 1 time in total.
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by ronniecoleman » Tue Dec 23, 2008 10:51 pm
The sum of the even numbers between 1 and n is 79*80, where n is an odd number, then n=?

1--n

no of even terms == (n-1)/ 2

Sum of AP == (n-1)/4 ( 2*2 + (n-1/2 - 1) 2 )
(n-1)(n+1)/ 4

(n-1)(n+1)/ 4 = 79*80

n= 159
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