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

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!

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!

All,

Thanks for your explanantions.


Thanks
Saurabh Malpani

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