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Senior Manager
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Joined: 04 Sep 2008
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Kudos [?]: 98 [0], given: 9

Location: Kolkata
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PS Squares [#permalink]

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New post 08 Jun 2009, 23:34
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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

Kudos [?]: 98 [0], given: 9

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Joined: 03 Jun 2009
Posts: 785

Kudos [?]: 883 [2], given: 56

Location: New Delhi
WE 1: 5.5 yrs in IT
Re: PS Squares [#permalink]

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New post 08 Jun 2009, 23:40
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=(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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Kudos [?]: 883 [2], given: 56

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Joined: 27 May 2009
Posts: 42

Kudos [?]: 230 [0], given: 3

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.

Kudos [?]: 230 [0], given: 3

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