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# Two different group of test takers received scores on the

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Intern
Joined: 26 Jul 2008
Posts: 4

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06 Aug 2008, 18:45
Two different group of test takers received scores on the GYZ test. Group A had a normal distribution with mean of 460 and a Standard Deviation of 20. Group B had a normal distribution with mean of 520 and a Standard Deviation of 40. If each group has the same number of test takers, what fractio of test takers who scored below 440 belong to Group B ??

1/9

1/8

1/6

4/17

4/21.

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Director
Joined: 23 Sep 2007
Posts: 761
Re: Standard Deviation and Normal Distribution  [#permalink]

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06 Aug 2008, 19:02
1
Guessing 4/21

this is somewhat of a convoluted question.

approx 68% falls between 1 SD of the average, so 32% outside of 1SD from average.
approx 95% falls between 2 SD of the average, so 5% outside of 2SD from average.

lets say 100 people in each group

in group A 16 people will be below 1 SD from average (32/2)

in group B 2.5 people will be below 2 SD from average (5/2)

So about 18.5 people (16 + 2.5) score lower than 440 from both groups

2.5/18.5 is somewhat closer to E than it it to D

not completely sure about my approximation.
Current Student
Joined: 11 May 2008
Posts: 551
Re: Standard Deviation and Normal Distribution  [#permalink]

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06 Aug 2008, 20:13
i think A..
the logic as above is same,..
but i have got my result on the basis that 68% is within the 1 st deviation
28% next , and 4% on the last..
BTW, what is the correct values.?
some books say 68%,28%,4%
others say 68, 27,and 5...
Current Student
Joined: 11 May 2008
Posts: 551
Re: Standard Deviation and Normal Distribution  [#permalink]

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08 Aug 2008, 10:11
hello... can the einsteins pitch in???
Director
Joined: 27 May 2008
Posts: 530
Re: Standard Deviation and Normal Distribution  [#permalink]

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08 Aug 2008, 11:13
First ot all i dont think its a GMAT question.. we are not supposed to know the properties of normal distribution..

i agree with gmatnub's approach .. the answer should be 2.5/18.5 actually 2.2/18 to be more accurate

closest option is B 1/8.
GMAT Tutor
Joined: 24 Jun 2008
Posts: 1345
Re: Standard Deviation and Normal Distribution  [#permalink]

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08 Aug 2008, 18:17
I haven't even read the question (but I trust Durgesh ), but you do not need to know anything about the properties of a normal distribution for the GMAT- and you definitely don't need to know what percentage of data points fall within one or two standard deviations in a normally distributed set of data.
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SVP
Joined: 29 Aug 2007
Posts: 2425
Re: Standard Deviation and Normal Distribution  [#permalink]

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08 Aug 2008, 18:23
IanStewart wrote:
I haven't even read the question (but I trust Durgesh ), but you do not need to know anything about the properties of a normal distribution for the GMAT- and you definitely don't need to know what percentage of data points fall within one or two standard deviations in a normally distributed set of data.

I am not sure about to what extent we need to understand these properties, but it won't harm if we remember these properties as well.

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Re: Standard Deviation and Normal Distribution &nbs [#permalink] 08 Aug 2008, 18:23
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# Two different group of test takers received scores on the

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