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Standard deviation problem [#permalink]
31 Jul 2009, 19:08

00:00

A

B

C

D

E

Difficulty:

(N/A)

Question Stats:

75% (01:10) correct
25% (01:04) wrong based on 3 sessions

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?

Re: Standard deviation problem [#permalink]
07 Aug 2009, 06:27

1

This post received KUDOS

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 % _________________

Bhushan S. If you like my post....Consider it for Kudos

Re: Standard deviation problem [#permalink]
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

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