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# To calculate

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Intern
Joined: 13 Feb 2009
Posts: 21

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24 Feb 2009, 03:20
1
What is value of
1 - 1/2 - 1/6 - 1/12 - 1/20 - 1/30 - 1/42 - 1/56 ?
A. 1/7
B. 1/6
C. 1/8
D. 1/9
E. 1/10

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SVP
Joined: 07 Nov 2007
Posts: 1732
Location: New York

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24 Feb 2009, 07:36
1
matematikconsultant wrote:
What is value of
1 - 1/2 - 1/6 - 1/12 - 1/20 - 1/30 - 1/42 - 1/56 ?
A. 1/7
B. 1/6
C. 1/8
D. 1/9
E. 1/10

(1 - 1/2) - (1/6+1/12) - (1/20+1/30) - (1/42+1/56)
=(1/2 - 1/4) - 1/12 - 1/24
=1/4 -1/8
=1/8
_________________

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VP
Joined: 05 Jul 2008
Posts: 1333

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24 Feb 2009, 14:21
initially thought of LCM but quickly noticed that subtracting 1/6 from 1/2 gave 1/3 and then subtracting 1/12 gave 1/4

So the answer would be 1/8
Manager
Joined: 26 Dec 2008
Posts: 57
Schools: Booth (Admit R1), Sloan (Ding R1), Tuck (R1)

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24 Feb 2009, 18:45
x2suresh wrote:
matematikconsultant wrote:
What is value of
1 - 1/2 - 1/6 - 1/12 - 1/20 - 1/30 - 1/42 - 1/56 ?
A. 1/7
B. 1/6
C. 1/8
D. 1/9
E. 1/10

(1 - 1/2) - (1/6+1/12) - (1/20+1/30) - (1/42+1/56)
=(1/2 - 1/4) - 1/12 - 1/24
=1/4 -1/8
=1/8

great approach, hats off to you. I am a newbie to the forum and have seen your posts in last 2-3 days -- you rock man!
Intern
Joined: 07 Oct 2008
Posts: 12

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24 Feb 2009, 19:40
I am a new person on the form..

1-1/2-1/6-1/12-1/20-1/30-1/42-1/56
=>1/2-1/4-1/12-1/24
3/24=1/8
Intern
Joined: 13 Feb 2009
Posts: 21

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25 Feb 2009, 03:46
1
1- (1-1/2) - (1/2-1/3) - (1/3-1/4) - (1/4-1/5) - (1/5-1/6) -(1/6-1/7) - (1/7-1/8) = 1/8
Manager
Joined: 01 Jan 2008
Posts: 220
Schools: Booth, Stern, Haas

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Updated on: 25 Feb 2009, 08:45
matematikconsultant wrote:
1- (1-1/2) - (1/2-1/3) - (1/3-1/4) - (1/4-1/5) - (1/5-1/6) -(1/6-1/7) - (1/7-1/8) = 1/8

I understood the approach you used, but how it helps to make it easier to solve?

thanks

Originally posted by kbulse on 25 Feb 2009, 05:57.
Last edited by kbulse on 25 Feb 2009, 08:45, edited 1 time in total.
Intern
Joined: 13 Feb 2009
Posts: 21

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25 Feb 2009, 06:37
Always, 1/(n(n+1)) = 1/n - 1/(n+1)

--== Message from GMAT Club Team ==--

This is not a quality discussion. It has been retired.

If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
Re: To calculate   [#permalink] 25 Feb 2009, 06:37
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# To calculate

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