Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

Standard Deviation Problem

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 43
Joined: Tue Sep 30, 2008 10:19 am
by dreamzz2010 » Fri Sep 25, 2009 4:48 pm
Two different groups of test takers received scores on the GXYZ standardized test. Group A’s scores had a normal distribution with a mean of 460 and a standard deviation of 20. Group B’s scores had a normal distribution with a mean of 520 and a standard deviation of 40. If each group has the same number of test takers, what fraction of the test-takers who scored below 440 belonged to Group B?

A. 1/9
B. 1/8
C. 1/6
D. 4/17
E. 4/21

Please explain how did you get to the answer. Will post the answer shortly.
Top
Join the discussion
Source: — Problem Solving |
Legendary Member
Posts: 882
Joined: Fri Feb 20, 2009 2:57 pmFollowed by: 1 member
Thanked: 15 times
GMAT Score:690

Re: Standard Deviation Problem

by crackgmat007 » Fri Sep 25, 2009 10:10 pm
dreamzz2010 wrote: Please explain how did you get to the answer.
Key to solve the question is - normal distribution.
Check this site https://en.wikipedia.org/wiki/Normal_distribution

We need to find out how many test takers scored less than 440. We get 2% in for B & 16% (14 + 2) for A. Hence 2/16 = 1/8. Choose B.

HTH
Top
Join the discussion

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 2623
Joined: Mon Jun 02, 2008 3:17 amFollowed by: 355 members
Location: Montreal
Thanked: 1090 times
GMAT Score:780

by Ian Stewart » Fri Sep 25, 2009 11:43 pm
As I explained here:

www.beatthegmat.com/pr-4-standard-devia ... 16015.html

the above is a very poorly designed question. The answer they give isn't even correct; to do this kind of question accurately, you need to consult a stats table, and in their solution, they've used values which are rounded off. That rounding error actually leads them to choose answer A when answer B is much closer to the correct value.

In any case, you don't need to know anything about this for the GMAT, and you'd need a book of stats tables to be able to answer it with any precision; otherwise you'll likely make the same rounding error that the question designer made.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

ianstewartgmat.com
Top
Join the discussion
Senior | Next Rank: 100 Posts
Posts: 43
Joined: Tue Sep 30, 2008 10:19 am

by dreamzz2010 » Sat Sep 26, 2009 5:47 am
Thanks crackgmat007 and Ian for putting in your words.

I also found the question bit awkward and so wanted to know about the quality of question. I picked it up from one of the princeton tests anf the OA is 1/9.

Though i guess after reading Ian's comments no one would want to waste time on this one :D
Top
Join the discussion