**Imp**Manhattan GMAT Word Translation Guide With STDV

[Saurabh Malpani]

Hi All,

I have a quick and a basic question about a statement---with in 2 standard deviation?>

The following question is from Manhattan GMAT guide--Word Translation Chapter 6 PAGE 87 QUESTION 10

a class mean score on a test was 60 and the Standard Deviation was 15. If Elena's score was withing 2 standard deviation what was the lowest Score she Could have received?

My question--> when it says with in two standard deviation the range shoud be 45<x<75? The answer provided assumes the range of 30<x<60

which one is correct!

Saurabh Malpani

[GMAT 5/18]

Saurabh,

In my experience, whenever a question asks for a figure "within 2 std. deviations", it is presumed that the data point lies within 2 std. deviations above the mean and 2 std. deviations below the mean. So, in your example, the answer would be 30<x<60.

If, for example, the question was:

"A class mean score on a test was 60 and the std. deviation 15. What could Elena's score range from if she scored within 1 std. deviation of the mean?"
Then, the answer would be 45<x<75.

I hope this helps!

[StaceyKoprince]

Yep, standard deviation always means both above and below the mean. So (for this problem) one standard deviation is +/-15 and 2 st.dev is +/-30. Good question!

[Saurabh Malpani]

All,

Thanks for your explanantions.


Thanks
Saurabh Malpani

Yep, standard deviation always means both above and below the mean. So (for this problem) one standard deviation is +/-15 and 2 st.dev is +/-30. Good question!

[srini091]

Stacy,

When they say that Elena's score was within 2 standard deviation from the mean, then her score could be -> Mean - (2 X SD) to Mean + (2 X SD) i.e 60-30 to 60+30. So, her score could be from 30 to 90. It cant be 30<x<60. Am I right?

When we say two SD from the mean, it is on both sides of the mean. Is this correct?

Thanks
Srini

[esledge]

Yes, Srini, you are correct. I think that was just a typo above.

Elena's range of possible scores is 60 +/- 30, which is 30 < x < 90. Thanks for clarifying.

[himanshu.hpr]

How is that possible for Leena to have score = 30 , when as per the question the range of scores of the entire class is between 45 and 75 , I mean she is part of class and yet her score is beyond the range of class ?

[tim]

have you read the entire thread? as near as i can tell, no one is saying the question mentions 45 or 75 at all..