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To calculate

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Intern
Joined: 13 Feb 2009
Posts: 21

Kudos [?]: 2 [1], given: 0

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24 Feb 2009, 03:20
1
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This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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

Kudos [?]: 2 [1], given: 0

SVP
Joined: 07 Nov 2007
Posts: 1795

Kudos [?]: 1032 [1], given: 5

Location: New York
Re: To calculate [#permalink]

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24 Feb 2009, 07:36
1
KUDOS
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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Kudos [?]: 1032 [1], given: 5

Intern
Joined: 13 Feb 2009
Posts: 21

Kudos [?]: 2 [1], given: 0

Re: To calculate [#permalink]

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25 Feb 2009, 03:46
1
KUDOS
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

Kudos [?]: 2 [1], given: 0

VP
Joined: 05 Jul 2008
Posts: 1403

Kudos [?]: 423 [0], given: 1

Re: To calculate [#permalink]

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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

Kudos [?]: 423 [0], given: 1

Manager
Joined: 26 Dec 2008
Posts: 58

Kudos [?]: 14 [0], given: 0

Schools: Booth (Admit R1), Sloan (Ding R1), Tuck (R1)
Re: To calculate [#permalink]

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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!

Kudos [?]: 14 [0], given: 0

Intern
Joined: 07 Oct 2008
Posts: 12

Kudos [?]: 3 [0], given: 0

Re: To calculate [#permalink]

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

Got the same answer
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

Kudos [?]: 3 [0], given: 0

Manager
Joined: 01 Jan 2008
Posts: 222

Kudos [?]: 61 [0], given: 2

Schools: Booth, Stern, Haas
Re: To calculate [#permalink]

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25 Feb 2009, 05:57
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

Last edited by kbulse on 25 Feb 2009, 08:45, edited 1 time in total.

Kudos [?]: 61 [0], given: 2

Intern
Joined: 13 Feb 2009
Posts: 21

Kudos [?]: 2 [0], given: 0

Re: To calculate [#permalink]

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

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Re: To calculate   [#permalink] 25 Feb 2009, 06:37
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