Material covered on Statistics/Quant

[wfung]

Hi,

I've been trying to look for an official GMAT page that mentions what specific topics are covered in the Quant section, specifically on Statistics. In the 5th edition of the Manhattan GMAT Word Problems Strategy Guide, it covers a basic understanding of standard deviation, however, I've come across some practice questions in the Official Guide where deeper knowledge of standard deviation is required the answer the question. Since the practice questions are old retired questions, I would like to know if the GMAT changed what is covered. Any guidance here is greatly appreciated.

Thanks!

[RonPurewal]

hi,
everything you need to know about the standard deviation on the gmat is given in this post:
post86007.html#p86007

as you'll see, it's not much in the way of raw knowledge. check it out.
you will have to be able to manipulate these concepts with skill and alacrity, but that doesn't change the fact that the required understanding comprises only basic concepts.

if you think there are any OG problems that require any further understanding than what's mentioned in the link, then you must be overcomplicating the issue in some way, since there are definitely no such problems.
if you think there are, then ...
* please reply with the problem numbers and edition number (12th or 13th). note: DO NOT post the problems themselves.
* please specify what you think you have to know, beyond the information mentioned in the link above, to solve those problems.
then, i'll explain (perhaps in general terms, so as to avoid divulging the GMAC content) why such further knowledge isn't actually necessary.

thanks.

[wfung]

Thanks for the link to the old post, which provided a great summary and good reassurance. However, I believe I do have one example where further explanation will be helpful - Problem #112, on page 167 (13th edition).

This question specifically mentions a population percentage that is within one SD from the mean. This is somewhat a familiar topic (previous to the GMAT), so when I drew a symmetric graph, I couldn't recall exactly what one SD looked like on the graph. Because of the question being asked, I would assume that knowledge of how one SD (or even two, three...) appears on a graph/distribution is needed to answer this question.

Hopefully I am incorrect, as I wouldn't want to memorize more than I need to :)

Thanks!

[jnelson0612]

Thanks for the link to the old post, which provided a great summary and good reassurance. However, I believe I do have one example where further explanation will be helpful - Problem #112, on page 167 (13th edition).

This question specifically mentions a population percentage that is within one SD from the mean. This is somewhat a familiar topic (previous to the GMAT), so when I drew a symmetric graph, I couldn't recall exactly what one SD looked like on the graph. Because of the question being asked, I would assume that knowledge of how one SD (or even two, three...) appears on a graph/distribution is needed to answer this question.

Hopefully I am incorrect, as I wouldn't want to memorize more than I need to :)

Thanks!

Nope, you don't need to know that! The problem tells you that 68 percent of the population is between -1 and +1 standard deviations from the mean. That means that one standard deviation encompasses half of that, or 34% of the population on each side. If I want to know the percent of a population that is below +1 standard deviation, I just take that 34% (from 0 to +1 SD) and add 50% (the half of the population that is below the midpoint--0 all the way through negative standard deviations). The answer is then 84%. Let me know if this is not clear.

[wfung]

After reviewing how -1 and +1 standard deviations appears on a symmetric graph, it's clear. When I first came across this question, I couldn't remember where 1 standard deviation is marked on a graph and when attempting to answer the question, ended up marking -0.5 standard deviation at the located where you would actually find -1 standard deviation, and similarly marking +0.5 standard deviation at the location of the actual position of +1 standard deviation. As you can imagine, not knowing this bit of detail would make this problem difficult to solve.

The Study Guide does a great job of covering the basics and advocating for a strong general understand, which definitely helps with most questions. But coming across a question like the example above, had me concerned that some additional coverage may be needed and was wondering if there's anything else to be aware of.

[jlucero]

Makes total sense to me. It's easy to think that there's something that you haven't learned about is on the test. But from every OG explanation and question we've come across, the info that Ron gave you is enough to solve If the GMAT does start to test an equation for standard deviation, we'll update our books then. But there's a larger point- if you've properly prepared yourself for the question types, you should be able to answer them with the skills you've learned. Your first instinct should be "how is this similar to something I have seen before" instead of, "well I never needed to know how to do this on other questions". (of course, that's easier said than done... I still will make mistakes while solving and think the OG messed up; so far the score is GMAT - all, Joe - 0)