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Std dev

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Re: Std dev

by dtweah » Mon May 18, 2009 12:14 pm
crackgmat007 wrote:Can someone solve this pls?
Mean: 8.1

1 SD .3

half SD .15

One and half SD .45

8.1 + .45= 8.55 one and half SD above the mean
8.1-.45= 7.65 one and half SD below the mean

Anything in the region [7.65, 8.55] will do. Only 11 are in this region. 7.51 is out of the interval, it is less than 7.65. Everything else is in.

This is a problem which can be missed because one does not organize his or her solution well. ALWAYS REMEMBER THE SD HAS TWO DIRECTIONS: AN ABOVE THE MEAN DIRECTION AND A BELOW THE MEAN DIRECTIOIN.
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by crackgmat007 » Mon May 18, 2009 12:47 pm
tx...i did not understand "1.5 standard deviations of the mean". that is why missed it. there was no word asking to multiply 1.5 with SD (such as times)
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