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The average (arithmetic mean) of a normal distribution of a [#permalink]
16 Aug 2010, 10:25

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Difficulty:

55% (hard)

Question Stats:

24% (01:13) correct
76% (00:50) wrong based on 29 sessions

The average (arithmetic mean) of a normal distribution of a school's test scores is 65, and standard deviation of the distribution is 6.5. A student scoring a 78 on the exam is in what percentile of the school?

But there’s something in me that just keeps going on. I think it has something to do with tomorrow, that there is always one, and that everything can change when it comes. http://aimingformba.blogspot.com

Re: Statistics question [#permalink]
16 Aug 2010, 10:50

2

This post received KUDOS

Expert's post

aiming4mba wrote:

The average (arithmetic mean) of a normal distribution of a school's test scores is 65, and standard deviation of the distribution is 6.5. A student scoring a 78 on the exam is in what percentile of the school?

a.63rd b.68th c.84th d.96th e.98th

You can solve this question if you know the 68.2-95.4-99.7 rule of normal distributions (though the normal distribution is an absolutely continuous probability distribution and this is not the case in the question): 78 is 2 SD from the mean (65+2*6.5=78), so below it are 95.4+\frac{100-95.4}{2}=97.7\approx{98} percent of data points, answer E. But don't worry about this question, normal distribution IS NOT tested on GMAT and you don't have to know this rule. _________________

Percentile --normal distribution [#permalink]
06 Feb 2011, 19:32

The average (arithmetic mean) of a normal distribution of a school's test scores is 65, and standard deviation of the distribution is 6.5. A student scoring a 78 on the exam is in what percentile of the school?

A 63rd percentile B 68th percentile C 84th percentile D 96th percentile E 98th percentile _________________

Consider me giving KUDOS, if you find my post helpful. If at first you don't succeed, you're running about average. ~Anonymous

Re: The average (arithmetic mean) of a normal distribution of a [#permalink]
07 Dec 2012, 12:19

Unfortunately or not, i have seen this question on Grockit. Its strange they are throwing such questions that do not have possibilities of being tested on the actual test.

The average (arithmetic mean) of a normal distribution of a [#permalink]
04 Jun 2013, 09:52

The average (arithmetic mean) of a normal distribution of a school's test scores is 65, and standard deviation of the distribution is 6.5. A student scoring a 78 on the exam is in what percentile of the school? A)63th percentile B)68th percentile C)84th percentile D)96th percentile E)98th percentile _________________

Re: The average (arithmetic mean) of a normal distribution of a [#permalink]
04 Jun 2013, 12:26

Stiv wrote:

The average (arithmetic mean) of a normal distribution of a school's test scores is 65, and standard deviation of the distribution is 6.5. A student scoring a 78 on the exam is in what percentile of the school? A)63th percentile B)68th percentile C)84th percentile D)96th percentile E)98th percentile

E...since the distribution of the curve is 2%,14%,34%,34%,14%,2%

Re: The average (arithmetic mean) of a normal distribution of a [#permalink]
04 Jun 2013, 14:16

Expert's post

Stiv wrote:

The average (arithmetic mean) of a normal distribution of a school's test scores is 65, and standard deviation of the distribution is 6.5. A student scoring a 78 on the exam is in what percentile of the school? A)63th percentile B)68th percentile C)84th percentile D)96th percentile E)98th percentile

Re: The average (arithmetic mean) of a normal distribution of a [#permalink]
04 Jun 2013, 20:48

Expert's post

Stiv wrote:

The average (arithmetic mean) of a normal distribution of a school's test scores is 65, and standard deviation of the distribution is 6.5. A student scoring a 78 on the exam is in what percentile of the school? A)63th percentile B)68th percentile C)84th percentile D)96th percentile E)98th percentile

This particular question is out of scope.

Note that mean and SD are tested on the GMAT but normal distributions are not. Then again, a question could mention that scores are normally distributed - the reason for that is that SD concept may not make sense for some distributions e.g. distributions with too much negative skewness etc. Hence they might mention that it is normally distributed for the discerning statistician. Normally, it can just be ignored. Focus only on the SD concepts. e.g. they could ask - which scores are 3 SD away from the mean? _________________