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# Is the standard deviation of ages of students in class A

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Is the standard deviation of ages of students in class A [#permalink]

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18 Feb 2004, 09:50
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Class..............Average Age........# of Students
A..................15 years.....................6
B..................16 years.....................12

Is the standard deviation of ages of students in class A greater than the standard deviation of the ages of students in class B?

(1) The maximum difference between the ages of any two students in class A is 1 year.

(2) No student in class B is more than 6 months older than any other student.
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18 Feb 2004, 10:29
C would be the answer
From 1) St. dev. for A is 1 yr. not suff. since we don't know the st. dev. of B
From 2) st. dev. for B is 1/2 yr. not suff. since we don't know the st. dev. of A

Both together we know their relative st. dev. and thus conclude that B's st. dev. is less. St. dev. is a measure of dispersion from the mean. Therefore, the averages of 15 for A and 16 for B have no incidence in selecting an answer regarding st. dev.
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18 Feb 2004, 13:39
Its C..

i) Gives us the deviation of Class A but no information pertaining to Class B -- Insufficient

ii) Gives us the deviations of Class B but no information pertaining to Class A --Insufficient

When data from the both options are combined we can conclude that Class B should have lesser standard deviation than Class A.

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Re: DS - Standard Deviation [#permalink]

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04 May 2010, 01:09
Hi,

In S1 and S2, we are given the age difference b/w any two students. Is it mean Std Deviation? I think it is Range rather than Std Dev.

Please clarify ans also give some more explanations.
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Re: DS - Standard Deviation [#permalink]

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05 May 2010, 21:57
E for me.

Standard deviation indicates the spread of data points around the mean. So the stem is asking whether the points in data set A cluster further away from the mean (on average) than the points in data set B.

Looking at the statements:

1) tells us that 1 is the maximum difference between the ages of any two students. This means that some students may be under 15, and some over 15, but since we need a final average that is exactly 15 years, the ages "under" will have to balance the ages "over. For example, you could have 3 students at 14.5 and 3 students at 15.5. But you could also have all students at exactly 15, which yields a st. dev. of 0.

2) is the same as 1, but with a range of 6 months max. Again, it could be 6 students at 3 months under 16, and 6 students at 3 months over 16. In this case, st. dev is > 0. But again, all ages could be exactly 16.

Since there is no information about the actual spread in either statement, and we only know that the range does not exceed a certain amount, the ans is E.
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Re: DS - Standard Deviation [#permalink]

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05 May 2010, 22:11
IMO E

if all the students have same age in both the classes, standard deviation is 0 for both.

In all other cases it may or may not be equal, hence insufficient.
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Re: DS - Standard Deviation [#permalink]

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06 May 2010, 06:10
gb82 wrote:
E for me.

Standard deviation indicates the spread of data points around the mean. So the stem is asking whether the points in data set A cluster further away from the mean (on average) than the points in data set B.

Looking at the statements:

1) tells us that 1 is the maximum difference between the ages of any two students. This means that some students may be under 15, and some over 15, but since we need a final average that is exactly 15 years, the ages "under" will have to balance the ages "over. For example, you could have 3 students at 14.5 and 3 students at 15.5. But you could also have all students at exactly 15, which yields a st. dev. of 0.

2) is the same as 1, but with a range of 6 months max. Again, it could be 6 students at 3 months under 16, and 6 students at 3 months over 16. In this case, st. dev is > 0. But again, all ages could be exactly 16.

Since there is no information about the actual spread in either statement, and we only know that the range does not exceed a certain amount, the ans is E.

Good point mate .. I missed while reading the question and answered C but after readin your explanation I understand why should be E

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Re: DS - Standard Deviation   [#permalink] 06 May 2010, 06:10
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# Is the standard deviation of ages of students in class A

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