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The mean score in a certain test is 80. If the test scores have a norm [#permalink]

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31 Jul 2009, 19:08

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The mean score in a certain test is 80. If the test scores have a normal distribution and the standarad distribution is 7, what percent of examinees score between 66 and 94?

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07 Aug 2009, 06:27

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Normal distribution says

1 sigma = 68% (34% on either side) population 2 sigma = 96% (14% on either side) population so 68% +14%x 2=96% 3 sigma = 99.99% (2% on either side) population so 96% + 2% x 2 ~ 99.99 %
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Re: The mean score in a certain test is 80. If the test scores have a norm [#permalink]

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19 Sep 2009, 06:06

The mean score in a certain test is 80. If the test scores have a normal distribution and the standarad distribution is 7, what percent of examinees score between 66 and 94?

A) 50% B) 68% C)82% D)96% E)98%

Soln: Here mean = 80 and standard deviation sig = 7 Since for a range of scores from 66 to 94, the scores vary between 2 * sig about mean that is from -2 * sig to +2 * sig for this range with normal distribution the percent of examinees is = 13.6 + 34.1 + 34.1 + 13.6 = 95.4 Approximately 96% Ans is D

Re: The mean score in a certain test is 80. If the test scores have a norm [#permalink]

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07 Nov 2015, 21:41

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This question is just testing standard knowledge of a normal distribution graph.

The mean=80, mean 50% of the data falls above and below this point,

When we consider 1 standard deviation on either side of it, we are cutting the data points of interest down to 34% on each side, or 68% between them

As for the question we are being asked about the range +/- 2 SD from the mean. This tests us just knowing that this represents 96% of the data of the data points, or 48% on either side of the mean.

Re: The mean score in a certain test is 80. If the test scores have a norm [#permalink]

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28 Nov 2015, 09:31

normal distribution represents the bell curve, in which 50% is above mean, and 50% below mean 34% lies within 1 standard deviation or mean+SD and mean-SD mean+-SD is 73 and 87. 68% of people have scores between 73 and 87 now, aprox. 14% is between (mean+2SD)-(Mean+SD), this is the same for mean minus 2 SD. Mean+2SD=94 Mean-2SD=66

ok, so in total, we have 68% + 28 = aprox. 98%.

gmatclubot

Re: The mean score in a certain test is 80. If the test scores have a norm
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