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Source: — Data Sufficiency |
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by ketkoag » Sun May 03, 2009 3:08 am
take 1: very simple , u know greatest, get the smallest coz nos are consecutive. hence suff.
take 2: find the sum of all the nos by 17.5 * 6 = 105
only one set of consecutive nos adds up to 105 and that is 15,16,17,18,19,20. hence suff.

thus D is the correct answer.
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by chetanojha » Sun May 03, 2009 3:24 am
Hi Ketkoag,

How do you know only one set ?(starting with 15) will add up to 105. Is there any formula or something...or have you straightway added the numbers together?
ketkoag wrote:only one set of consecutive nos adds up to 105 and that is 15,16,17,18,19,20. hence suff.

thus D is the correct answer.
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by ketkoag » Sun May 03, 2009 5:34 am
there is no as such formula for this, just try to add consecutive nos from any other set and lemme know if u get 105 . the above set is the only set. :)
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by Objectivo » Sun May 03, 2009 5:38 am
Hi ketkoag,
You could put this into a simple formula With the thing we're looking for being 6 consecutive positive integers, you could write a formula such as:

x+(x+1)+(x+2)+(x+3)+(x+4)+(x+5)=105
=> 6x+15=105
=> 6x=105-15
=> 6x=90
=> x=15

This means that 15 is the lowest of the 6, hence the others are 17, 18, 19 and 20.
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