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George scored 85 on an exam. Did George do better than 90

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josemnz83
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George scored 85 on an exam. Did George do better than 90 [#permalink] New post   07 Jul 2013, 08:57
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George scored 85% on an exam. Did George do better than 90% of his classmates on the test?
1) The mean score on the test was 80%.
2) The stardard deviation is 2.


I understand that George's score is 2.5 deviations above the mean. How does that give me any information as to how his classmates did?

On the explanation, it notes that George did better than 95% of his classmates. Please explain.
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Vips0000
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Re: George scored 85 on an exam. Did George do better than 90 [#permalink] New post   07 Jul 2013, 09:04
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josemnz83 wrote:
George scored 85% on an exam. Did George do better than 90% of his classmates on the test?
1) The mean score on the test was 80%.
2) The stardard deviation is 2.


I understand that George's score is 2.5 deviations above the mean. How does that give me any information as to how his classmates did?

On the explanation, it notes that George did better than 95% of his classmates. Please explain.

Its more of a stats question that DS.

From question we know that George scored 85%.

i. mean score 80%.. we know george scored better than average but thats all. Not sufficient
ii. standard deviation is 2.. nothing can be inferred from this.. Not sufficient.

However, if you combine these two information, (and little knowledge of basic statistics)
you know that 1 standard deviation from mean covers roughly 68% and 2 standard deviation covers roughly 95%.

George's score is more than 2 standard deviation higher than mean.. and therefore,it implies that it is more than 95% of students. Sufficient.

Ans C it is.
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Bunuel
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Re: George scored 85 on an exam. Did George do better than 90 [#permalink] New post   07 Jul 2013, 09:12
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Vips0000 wrote:
josemnz83 wrote:
George scored 85% on an exam. Did George do better than 90% of his classmates on the test?
1) The mean score on the test was 80%.
2) The stardard deviation is 2.


I understand that George's score is 2.5 deviations above the mean. How does that give me any information as to how his classmates did?

On the explanation, it notes that George did better than 95% of his classmates. Please explain.

Its more of a stats question that DS.

From question we know that George scored 85%.

i. mean score 80%.. we know george scored better than average but thats all. Not sufficient
ii. standard deviation is 2.. nothing can be inferred from this.. Not sufficient.

However, if you combine these two information, (and little knowledge of basic statistics)
you know that 1 standard deviation from mean covers roughly 68% and 2 standard deviation covers roughly 95%.

George's score is more than 2 standard deviation higher than mean.. and therefore,it implies that it is more than 95% of students. Sufficient.

Ans C it is.


68.2-95.4-99.7 rule of normal distributions is not tested on GMAT.

Next, even if it were tested, the question still would be flawed as the normal distribution is an absolutely continuous probability distribution and I don't think that we can apply its three-sigma rule (68.2-95.4-99.7 rule), as intended, to solve this question which is not continuous distribution.

So I wouldn't worry at all about this question.

Hope it helps.
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Re: George scored 85 on an exam. Did George do better than 90 [#permalink] New post   07 Jul 2013, 09:29
Bunuel wrote:
Vips0000 wrote:
josemnz83 wrote:
George scored 85% on an exam. Did George do better than 90% of his classmates on the test?
1) The mean score on the test was 80%.
2) The stardard deviation is 2.


I understand that George's score is 2.5 deviations above the mean. How does that give me any information as to how his classmates did?

On the explanation, it notes that George did better than 95% of his classmates. Please explain.

Its more of a stats question that DS.

From question we know that George scored 85%.

i. mean score 80%.. we know george scored better than average but thats all. Not sufficient
ii. standard deviation is 2.. nothing can be inferred from this.. Not sufficient.

However, if you combine these two information, (and little knowledge of basic statistics)
you know that 1 standard deviation from mean covers roughly 68% and 2 standard deviation covers roughly 95%.

George's score is more than 2 standard deviation higher than mean.. and therefore,it implies that it is more than 95% of students. Sufficient.

Ans C it is.


68.2-95.4-99.7 rule of normal distributions is not tested on GMAT.

Next, even if it were tested, the question still would be flawed as the normal distribution is an absolutely continuous probability distribution and I don't think that we can apply its three-sigma rule (68.2-95.4-99.7 rule), as intended, to solve this question which is not continuous distribution.

So I wouldn't worry at all about this question.

Hope it helps.


Well, I wouldnt say that we cant apply normal distribution rule as usually for any large distribution rules of normal distribution are applied (decision making in every day business and consulting problems/sample-estimation etc)

With the given question- you could definitely apply the knowledge. Though I agree, its not a DS question for GMAT.
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Re: George scored 85 on an exam. Did George do better than 90 [#permalink] New post   07 Jul 2013, 09:33
Expert Reply
Vips0000 wrote:
Bunuel wrote:
Vips0000 wrote:
Its more of a stats question that DS.

From question we know that George scored 85%.

i. mean score 80%.. we know george scored better than average but thats all. Not sufficient
ii. standard deviation is 2.. nothing can be inferred from this.. Not sufficient.

However, if you combine these two information, (and little knowledge of basic statistics)
you know that 1 standard deviation from mean covers roughly 68% and 2 standard deviation covers roughly 95%.

George's score is more than 2 standard deviation higher than mean.. and therefore,it implies that it is more than 95% of students. Sufficient.

Ans C it is.


68.2-95.4-99.7 rule of normal distributions is not tested on GMAT.

Next, even if it were tested, the question still would be flawed as the normal distribution is an absolutely continuous probability distribution and I don't think that we can apply its three-sigma rule (68.2-95.4-99.7 rule), as intended, to solve this question which is not continuous distribution.

So I wouldn't worry at all about this question.

Hope it helps.


Well, I wouldnt say that we cant apply normal distribution rule as usually for any large distribution rules of normal distribution are applied (decision making in every day business and consulting problems/sample-estimation etc)

With the given question- you could definitely apply the knowledge. Though I agree, its not a DS question for GMAT.


Well, for one we don't know how large distribution we have (we cannot assume). Also, we are not told that the we in fact have a normal distribution.
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Re: George scored 85 on an exam. Did George do better than 90 [#permalink] New post   07 Jul 2013, 09:48
Bunuel wrote:
Vips0000 wrote:
Bunuel wrote:

68.2-95.4-99.7 rule of normal distributions is not tested on GMAT.

Next, even if it were tested, the question still would be flawed as the normal distribution is an absolutely continuous probability distribution and I don't think that we can apply its three-sigma rule (68.2-95.4-99.7 rule), as intended, to solve this question which is not continuous distribution.

So I wouldn't worry at all about this question.

Hope it helps.


Well, I wouldnt say that we cant apply normal distribution rule as usually for any large distribution rules of normal distribution are applied (decision making in every day business and consulting problems/sample-estimation etc)

With the given question- you could definitely apply the knowledge. Though I agree, its not a DS question for GMAT.


Well, for one we don't know how large distribution we have (we cannot assume). Also, we are not told that the we in fact have a normal distribution.


You are the boss dude.. Usually a class is large enough to apply normal distribution rules.. But again you right in stating thats an assumption... you could as well have a class with 10 people.
I would say, we can create a confidence interval and then probably claim with 95% confidence level that C is the answer.. :twisted:
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Bunuel
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Re: George scored 85 on an exam. Did George do better than 90 [#permalink] New post   07 Jul 2013, 09:50
Expert Reply
Vips0000 wrote:
Bunuel wrote:
Vips0000 wrote:

Well, I wouldnt say that we cant apply normal distribution rule as usually for any large distribution rules of normal distribution are applied (decision making in every day business and consulting problems/sample-estimation etc)

With the given question- you could definitely apply the knowledge. Though I agree, its not a DS question for GMAT.


Well, for one we don't know how large distribution we have (we cannot assume). Also, we are not told that the we in fact have a normal distribution.


You are the boss dude.. Usually a class is large enough to apply normal distribution rules.. But again you right in stating thats an assumption... you could as well have a class with 10 people.
I would say, we can create a confidence interval and then probably claim with 95% confidence level that C is the answer.. :twisted:


It's a poor quality question. Topic locked.
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George scored 85% on an exam. [#permalink] New post   17 Jul 2013, 05:09
George scored 85% on an exam. Did George do better than 90% of his classmates on the test?
1) The median score on the test was 80%.
2) The stardard deviation is 2.
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Re: George scored 85% on an exam. [#permalink] New post   17 Jul 2013, 05:47
Expert Reply
espa wrote:
George scored 85% on an exam. Did George do better than 90% of his classmates on the test?
1) The median score on the test was 80%.
2) The stardard deviation is 2.


Merging topics. Please refer to the solutions above.
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Re: George scored 85% on an exam. [#permalink]
17 Jul 2013, 05:47
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