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Principal of a school recorded the number of students in each of 15 cl

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Principal of a school recorded the number of students in each of 15 cl  [#permalink]

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New post 25 Oct 2018, 02:22
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A
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E

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Principal of a school recorded the number of students in each of 15 classes. What was the standard deviation of the numbers of students in the 15 classes?

(1) The average (arithmetic mean) number of students for all the classes was 30.
(2) Each classes had the same number of students.

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Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

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New post 25 Oct 2018, 04:18
The answer is E.

This question is resolved using the logic of standard deviation - SD is a measure of how spread out an average is. To find it, we need info about the variance of the values being checked, or the values themselves (the number of students in each class). Without that information, finding standard deviation is impossible.
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Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

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New post 25 Oct 2018, 06:34

Solution


Given:
    • The total number of classes = 15

To find:
    • The standard deviation of the number of students in the 15 classes

Analysing Statement 1
    • Given that the average number of students for all the classes = 30

But, we do not have any information about the number of students in each class.

Therefore, Statement 1 alone is not sufficient to answer this question.

Analysing Statement 2
    • Given that each class had the same number of students
      o Thus, deviation = 0

Therefore, Statement 2 alone is sufficient to answer this question

Hence, the correct answer is Option B

Answer: B

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Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

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New post 25 Oct 2018, 07:33
The standard deviation of the number of students in the 15 classes

Given that the average number of students for all the classes = 30

But, we do not have any information about the number of students in each class.

Therefore, Statement 1 alone is not sufficient to answer this question.



Therefore, Statement 2 alone is sufficient to answer this question
Option B
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Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

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New post 25 Oct 2018, 08:01
Q: std. deviation between # students in 15 classes

S1: avg
S2: each class same # students

S1: insufficient --> average is not enough to determine std. Says nothing about dispersion.

S2: each class same # students --> so difference of them from median 0 , # students class A = # students each other class = avg. the same too , so data points do not deviate from mean = Standard deviation 0


Hence, B imo.
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Re: Principal of a school recorded the number of students in each of 15 cl  [#permalink]

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New post 25 Oct 2018, 15:14
If the number of students in each class is the same; there is no deviation between the classes. In other words, zero deviation.

Answer: B
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Re: Principal of a school recorded the number of students in each of 15 cl   [#permalink] 25 Oct 2018, 15:14
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Principal of a school recorded the number of students in each of 15 cl

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