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PS Squares

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Manager
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Joined: 04 Sep 2008
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PS Squares  [#permalink]

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New post 08 Jun 2009, 23:34
00:00
A
B
C
D
E

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1² - 2² + 3² - 4² + ________ - 10² = ?

A. 45

B. - 45

C. - 54

D. - 55

Doea anyone have the proper techinique of solving this

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rampuria

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Re: PS Squares  [#permalink]

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New post 08 Jun 2009, 23:40
2
=(1-2)(1+2) + (3-4)(3+4) + ...... (7-8)(7+8) + (9-10)(9+10)
= -3 -7 - 11 - 15 - 19
= -55

Hence E
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Re: PS Squares  [#permalink]

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New post 09 Jun 2009, 02:42
rampuria wrote:
1² - 2² + 3² - 4² + ________ - 10² = ?

A. 45

B. - 45

C. - 54

D. - 55

Doea anyone have the proper techinique of solving this


since 1² - 2² = -(1+2)
so the total can be :
-(1+2+3+...10)
which can be calculated by the formula(some of arithmatic progression )
-(n(n+1)/2) for n=10
so it's -55 and hence D.

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

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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: PS Squares &nbs [#permalink] 09 Jun 2009, 02:42
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