• Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep

need the standard deviation for dummies book

This topic has 1 expert reply and 1 member reply
allenkt Senior | Next Rank: 100 Posts Default Avatar
Joined
14 Apr 2007
Posted:
36 messages

need the standard deviation for dummies book

Post Sun May 06, 2007 1:29 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    I have a very basic understanding of standard deviation but apparently I need more. I've taken both of the GMATPrep tests and both times a standard deviation question appeared near the beginning. And both times I was stumped.

    Pretty much all I know about standard deviation is that it is a way to express how far away from the mean a value is. But I don't understand how to manipulate it or how other numbers would affect it. The first question on the quantitative section was something like I had a certain set of numbers and the mean was 33. Then what numbers would need to be added to change the standard deviation. Obviously that's not exactly it but that is the kind of information I'm clueless about.

    Can someone point me to a resource that will help me gain a basic understanding of this concept?



    Last edited by allenkt on Mon May 07, 2007 6:41 am; edited 1 time in total

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    allenkt Senior | Next Rank: 100 Posts Default Avatar
    Joined
    14 Apr 2007
    Posted:
    36 messages
    Post Mon May 07, 2007 6:40 am
    To answer my own question, I did find some helpful information in the math review of OG 11. Here is what I learned, hopefully this will help others who are struggling as I was:

    To find the standard deviation:

    1) find the mean of the numbers
    2) find the difference between each number and the mean
    3) square each number from step 2
    4) find the average of all the numbers in step 3
    5) take the nonnegative square root of that average

    The number from step 5 = standard deviation.

    I doubt I would have to actually calculate the sd in a problem, so the key point to remember is that the standard deviation depends most on values that are farthest from the mean. Adding numbers to a set that are close to the mean will not change the standard deviation very much. Adding numbers that are far from the mean will change the standard deviation more.

    Hope that helps.

    GMAT/MBA Expert

    Stacey Koprince GMAT Instructor
    Joined
    27 Dec 2006
    Posted:
    2228 messages
    Followed by:
    679 members
    Thanked:
    639 times
    GMAT Score:
    780
    Post Thu May 17, 2007 7:19 pm
    Yeah, I've never seen them ask us to calculate SD in a problem - it would take too long.

    Also, FYI, we're unlikely to see more than one SD question (if any) on the test - I definitely applaud you for figuring this out since you saw one on each test - but for others, studying SD may not be the best use of time. This falls into the "very infrequent" category.

    Also FYI - it actually doesn't matter too much even if the question is towards the beginning. One question won't make or break a score.

    _________________
    Please note: I do not use the Private Messaging system! I will not see any PMs that you send to me!!

    Stacey Koprince
    GMAT Instructor
    Director of Online Community
    Manhattan GMAT

    Contributor to Beat The GMAT!

    Learn more about me

    Free Manhattan Prep online events - The first class of every online Manhattan Prep course is free. Classes start every week.

    Best Conversation Starters

    1 Vincen 132 topics
    2 lheiannie07 69 topics
    3 LUANDATO 61 topics
    4 Roland2rule 42 topics
    5 ardz24 40 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    134 posts
    2 image description EconomistGMATTutor

    The Economist GMAT Tutor

    117 posts
    3 image description GMATGuruNY

    The Princeton Review Teacher

    117 posts
    4 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    109 posts
    5 image description DavidG@VeritasPrep

    Veritas Prep

    76 posts
    See More Top Beat The GMAT Experts