Practice Exam #2 Question #1

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fangtray: Master | Next Rank: 500 Posts; Posts: 273; Joined: Thu Sep 08, 2011 6:50 amFollowed by: 3 members; Thanked: 5 times

by fangtray » Sun Apr 22, 2012 3:54 am

The arithmetic mean and standard deviation of a certain normal distribution are 13.5 and 1.5 respectively What value is exactly 2 standard deviations from the mean?

a. 10.5
b. 11.0
c. 11.5
d. 12.0
e. 12.5

I'm not even really sure what the question is asking. Does BTG have a good article on standard deviation?

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Source: Beat The GMAT — Problem Solving | Sun Apr 22, 2012 3:54 am

Shalabh's Quants: Master | Next Rank: 500 Posts; Posts: 134; Joined: Fri Apr 06, 2012 3:11 amFollowed by: 5 members; Thanked: 35 times

by Shalabh's Quants » Sun Apr 22, 2012 6:12 am

fangtray wrote:The arithmetic mean and standard deviation of a certain normal distribution are 13.5 and 1.5 respectively What value is exactly 2 standard deviations from the mean?

a. 10.5
b. 11.0
c. 11.5
d. 12.0
e. 12.5

I'm not even really sure what the question is asking. Does BTG have a good article on standard deviation?

Well SD is a measure of deviation from mean. It is an indicator how far data values are dispersed vis-a-vis mean.

Question asks for values 2 SD times deviated from mean.

So the values = Mean + 2.SD = 13.5 + 2 * 1.5 = 10.5 & 16.5. Ans A.

Shalabh Jain,
e-GMAT Instructor

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neelgandham: Community Manager; Posts: 1060; Joined: Fri May 13, 2011 6:46 amFollowed by: 52 members; Location: Utrecht, The Netherlands; Thanked: 318 times

by neelgandham » Sun Apr 22, 2012 7:25 am

I'm not even really sure what the question is asking.

Before I explain, Can I request you to completely(Yes, completely) erase your brain cache. Good! Now read the below question.

The values of X and Y are 13.5 and 1.5 respectively. What value is exactly 2*Y units from X on the number line?
Try to solve it. Yes! this question and the question posed by you(with the statistics jargon) are one and the same.

Does BTG have a good article on standard deviation?

Yes, it definitely has one. Here it is - https://www.beatthegmat.com/mba/2010/10/ ... -deviation.
You can also find a few articles here - https://www.beatthegmat.com/mba/category ... ibrary-tag
You can also find a lot of wonderful GMAT articles here - https://www.beatthegmat.com/mba/category/tags

Let me know if you still need help. Happy to help.

Anil Gandham
Welcome to BEATtheGMAT | Photography | Getting Started | BTG Community rules | MBA Watch
Check out GMAT Prep Now's online course at https://www.gmatprepnow.com/

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minhchau1986: Junior | Next Rank: 30 Posts; Posts: 29; Joined: Thu Dec 25, 2008 2:55 pm; Thanked: 2 times

by minhchau1986 » Sun Apr 22, 2012 11:12 am

Normal distribution represents the belt curve. 95% of data lies on the 2 standard deviation. That is all but dont need to know to solve this problem for sure.

We will have the value in the range from -2 sd to +2 sd. So

13.5-2x1.5=10.5 or
13.5+2x 1.5=16.5

10.5 is valid answer or A

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fangtray: Master | Next Rank: 500 Posts; Posts: 273; Joined: Thu Sep 08, 2011 6:50 amFollowed by: 3 members; Thanked: 5 times

by fangtray » Sun Apr 22, 2012 3:58 pm

neelgandham wrote:
I'm not even really sure what the question is asking.
Before I explain, Can I request you to completely(Yes, completely) erase your brain cache. Good! Now read the below question.

The values of X and Y are 13.5 and 1.5 respectively. What value is exactly 2*Y units from X on the number line?
Try to solve it. Yes! this question and the question posed by you(with the statistics jargon) are one and the same.

Does BTG have a good article on standard deviation?
Yes, it definitely has one. Here it is - https://www.beatthegmat.com/mba/2010/10/ ... -deviation.
You can also find a few articles here - https://www.beatthegmat.com/mba/category ... ibrary-tag
You can also find a lot of wonderful GMAT articles here - https://www.beatthegmat.com/mba/category/tags

Let me know if you still need help. Happy to help.

oh wow, what an easy question, i just misunderstood it. thx!

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GMAT/MBA Expert

Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Sun Apr 22, 2012 5:26 pm

fangtray wrote:The arithmetic mean and standard deviation of a certain normal distribution are 13.5 and 1.5 respectively What value is exactly 2 standard deviations from the mean?

a. 10.5
b. 11.0
c. 11.5
d. 12.0
e. 12.5

I'm not even really sure what the question is asking. Does BTG have a good article on standard deviation?

The value which is exactly two SD less than the mean implies mean - 2 * SD = 13.5 - 2 * 1.5 = 10.5

The correct answer is A.

Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

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