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please be the fifth

by sanju09 » Sat Feb 13, 2010 12:17 am
For a class test, the mean score was 65, the median score was 71, and the standard deviation of the scores was 7. The teacher decided to add 5 points to each score due to a grading error. Which of the following statements must be true for the new scores?

I. The new mean score is 70.
II. The new median score is 76.
III. The new standard deviation of the scores is 12.

[spoiler]I'm to prepare the five choices to this question, with first four being the real GMAT trap. So, please be the fifth, the instructors.[/spoiler]
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by ajith » Sat Feb 13, 2010 7:03 am
sanju09 wrote:For a class test, the mean score was 65, the median score was 71, and the standard deviation of the scores was 7. The teacher decided to add 5 points to each score due to a grading error. Which of the following statements must be true for the new scores?

I. The new mean score is 70.
II. The new median score is 76.
III. The new standard deviation of the scores is 12.

[spoiler]I'm to prepare the five choices to this question, with first four being the real GMAT trap. So, please be the fifth, the instructors.[/spoiler]
I and II must be true

I - Mean will be shifted by 5 since every students score will be increased by 5
II - since everybody received 5 extra points the order remains the same; the median will be increased by 5

III - Since all the numbers increased by the same amount it doesnt increase variation. Standard deviation will remain the same
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