5 lb book of gre-advanced quant

[gbd97]

I have a confusion in 5 lb book of gre, page -1013, question number-47
standard deviation is asked to find out, I got 17.5
but the answer is given 36.6 and also the explanation given is not likely to be correct. Can anyone clarify me?

[gbd97]

the question was:
set s=-1,4,30,-21. If the mean is 4, then the standard deviation , rounded to nearest tenth, is equal to what?

[tommywallach]

Hey Gbd,

set s=-1,4,30,-21.

Average = Sum/# of terms

Average = -1 + 4 + 30 + -21 = 12

Average = 12/4 = 3 <-- You said it was 4?

Now, to find the SD, we subtract the mean from each term, and square the result:

(-1) - 3 = -4 --> squared = 16
4 - 3 = 1 --> squared = 1
30 - 3 = 27 --> squared = 729
-21 - 3 = -24 --> squared = 576

Now we find the average of those numbers:

(16 + 1 + 729 + 576)/4 = 1322/4 = 330.5

Finally, we square root the result = 18.17

To the nearest tenth = 18.2

Does this look correct to you? I don't have the book in front of me, but that ought to be the answer...

-t

[gbd97]

hi tommy,
the question was exactly what i wrote in previous post.
So the question as well as explanation is likely to be incorrect.
Is there any errata for 5 lb book?- so that error can be posted .
thank you.

[tommywallach]

Hey GBD,

Apparently so. That's our first edition of that book and, as you can see, it's 5lbs. So it's almost inevitable a few mistakes snuck in there. Thanks for the catch. I'll let the necessary people know. : )

-t

[gbd97]

hi Tommy,
I have another inquiry regarding 5 lb book of gre supplement : where is the video instruction? i do not find it. I just got the challenge problem archive!
thank you.

[tommywallach]

Hey GBD,

I'm not sure what video instruction you mean. Recordings of classes and such are in your student center, but those come with a full-on course, not just buying a book. If you're referring to something else, the best thing to do is call Student Services at this number, and they can talk you through tech issues: 212-721-7400.

-t