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apoorva_srivastva
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Post subject: Standard Deviation - Again :( HELPPPPPP!!  Posted: Fri Jul 17, 2009 12:42 pm |
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Posts: 27
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A set of data consists of the following 5 numbers: 0,2,4,6 and 8.Which two numbers,if added to create a set of 7 numbers will result in a new standard deviation that is close to the standard deviation for the original 5 numbers?
A.-1 and 9
B. 4 and 4
C. 3 and 5
D. 2 and 6
E. 0 and 8
My approach:
Though Not sure if a shorter method available but please advice if this one works!!
0 2 4 6 8 ..................mean ===>4
variance= ( X-m)^2 /N which is 2*(2^2+ 4^2)/5 = 8
now we need to add 2 numbers and be as close as posible to the original SD which is sqrt(8)
assume A as the sum of the new variances ....
A= (X6 - mean)^2 + (X7 - mean)^2
we know that
(40 + A)/7 = 8
(X6 - mean)^2 + (X7 - mean)^2= 16
(X6 - 4)^2 + (X7 - 4)^2 = 16
by looking into the choices..... i get from choice D ==>8
and from choice E ==> 32
both 32 and 8 are equidistant from 16
SO MY QUESTION IS WHICH ONE SHOULD I GO FOR :O
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ashish.jere
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Post subject: Re: Standard Deviation - Again :( HELPPPPPP!! Posted: Sat Jul 18, 2009 3:07 am |
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imo.
we have pick an answer choice that adds least to both numerator and denominator.
so, i picked (C). what is the answer?
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apoorva_srivastva
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Post subject: Re: Standard Deviation - Again :( HELPPPPPP!! Posted: Sat Jul 18, 2009 1:55 pm |
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selva.e
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Post subject: Re: Standard Deviation - Again :( HELPPPPPP!! Posted: Sun Jul 19, 2009 12:14 am |
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B
pretty straight forward approach.
Standard deviation = deviation from the mean.
from the given data 0,2,4,6,8... mean is 4
So for the least deviation from mean 4, if we choose both the number as 4, the average will not change eventually S.D will not change also.. :-)
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apoorva_srivastva
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Post subject: Re: Standard Deviation - Again :( HELPPPPPP!! Posted: Sun Jul 19, 2009 3:57 pm |
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selva.e wrote: B
pretty straight forward approach.
Standard deviation = deviation from the mean.
from the given data 0,2,4,6,8... mean is 4
So for the least deviation from mean 4, if we choose both the number as 4, the average will not change eventually S.D will not change also.. :-) OA is D TUTORS PLEASE HELPPPPPP
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mxs2009
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Post subject: Re: Standard Deviation - Again :( HELPPPPPP!! Posted: Mon Jul 20, 2009 5:47 am |
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Technically, E is closer, but more importantly, I'm having a hard time believing this is a GMAT prep question for the reasons mentioned in the original post. can you provide a screenshot please?
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apoorva_srivastva
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Post subject: Re: Standard Deviation - Again :( HELPPPPPP!! Posted: Mon Jul 20, 2009 9:18 am |
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mxs2009 wrote: Technically, E is closer, but more importantly, I'm having a hard time believing this is a GMAT prep question for the reasons mentioned in the original post. can you provide a screenshot please? I dont know how to get a screen shot!!! please let tell me how to do that!!!
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RonPurewal
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Post subject: Re: Standard Deviation - Again :( HELPPPPPP!! Posted: Tue Jul 21, 2009 7:32 pm |
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Posts: 7146
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yeah, i concur with the original poster.
if this IS indeed a gmatprep question, then it absolutely runs counter to EVERY trend that has EVER appeared in gmat standard deviation questions. every one of them.
also, if this is a gmatprep question, then there is ABSOLUTELY NO WAY that it contains the words "is close to", since those words have no precise meaning at all.
if it said "closest to", then that would be better.
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in any case, please post a screen shot if this is really a gmat question.
first, get a screen shot. this varies by computer, but it should be simple. just google "take screen shot" along with the name of your operating system (windows or whatever).
then, go to an image hosting site, such as postimage.org or xs.to, and post the image. take the link that you'll get, and post it here.
thanks.
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