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The students in two classes of "Underachiever" high school took a test

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The students in two classes of "Underachiever" high school took a test [#permalink]

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New post 26 Sep 2016, 03:12
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The students in two classes of "Underachiever" high school took a test. x, a, and c are, respectively, the standard deviation, median and the mean of the test scores of the students in class X. y, b, and d are, respectively, the standard deviation, median and mean of the test scores of the students in class Y. Is x>y?

(1) a < b

(2) c < d
[Reveal] Spoiler: OA

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Re: The students in two classes of "Underachiever" high school took a test [#permalink]

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New post 27 Sep 2016, 02:05
Even if we know mean and median, to definitely derive SD we should know individual data of each class

Hence SD can not be determined. I choose E
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Re: The students in two classes of "Underachiever" high school took a test [#permalink]

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New post 27 Sep 2016, 11:30
Statement 1 insufficient because median doesn't tell us anything about the number in the set and the values in the set
Statement 2 insufficient because the mean doesn't tell us the number in the sets of their values

When we combine them same issue

IMO E
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The students in two classes of "Underachiever" high school took a test [#permalink]

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New post 27 Sep 2016, 12:54
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Given: Two classes X and Y
X: x (standard deviation), a (median), and c (mean)
Y: y (standard deviation), b (median), and d (mean)

Is x>y?

(1) a < b
Let's assume
Scores in class X: 10, 20, 30
Scores in class Y: 20, 30,40
a = 20 , b = 30 ==> a<b
standard deviation will be same in both cases (evenly spaced set with same difference) ==> x=y=10, Is x>y = NO

Now assume scores in class Y: 24,25,26
b=25 ==> Now the standard deviation is 1, x=10 and y=1, Is x>y = YES

Hence not sufficient.

(2) c < d
Consider the above scenarios
We will get both answers (yes and no) to "Is x>y" in this case

(1)+(2) is not adding anything new, so it won't be sufficient

Hence E
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Re: The students in two classes of "Underachiever" high school took a test [#permalink]

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New post 09 Mar 2017, 23:26
Standard Deviation is the distance of the scores from the mean.So getting the mean or median will not give any information on SD.Hence answer is E.
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Re: The students in two classes of "Underachiever" high school took a test [#permalink]

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New post 15 Dec 2017, 06:23
deepthit wrote:
Even if we know mean and median, to definitely derive SD we should know individual data of each class

Hence SD can not be determined. I choose E


Not necessarily! If we knew that the sets had the same number and were evenly spaced, we could find the answer. In this case (statements), x<y.
Re: The students in two classes of "Underachiever" high school took a test   [#permalink] 15 Dec 2017, 06:23
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The students in two classes of "Underachiever" high school took a test

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