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Two different group of test takers received scores on the
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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.

Please help solve this...

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Re: Standard Deviation and Normal Distribution
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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

Re: Standard Deviation and Normal Distribution
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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...

Re: Standard Deviation and Normal Distribution
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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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Re: Standard Deviation and Normal Distribution
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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.

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

This is not a quality discussion. It has been retired.

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.