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Practice Exam #2 Question #1

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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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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.
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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.
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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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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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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.
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