Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 21 Aug 2014, 20:29

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

normal distribution

 Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
Intern
Joined: 23 Nov 2009
Posts: 5
Followers: 0

Kudos [?]: 0 [0], given: 5

normal distribution [#permalink]  07 Dec 2009, 17:08
00:00

Difficulty:

(N/A)

Question Stats:

100% (03:00) correct 0% (00:00) wrong based on 5 sessions
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-1/8
b-1/9
c-1/6
d-4/17
e-4/21
Manager
Joined: 29 Jul 2009
Posts: 225
Followers: 3

Kudos [?]: 42 [1] , given: 6

Re: normal distribution [#permalink]  07 Dec 2009, 20:46
1
KUDOS
1/9 I think. This could be kinda tricky even if you know the normal distribution, bc of the estimation. I did it this way. 1 std deviation away to the left would be all the people who got less than 440 in group A, which means 14% (1 std below)+2% (2 std below)=16% in the Group A. Now for Group B, it's two std deviations to the left. So about 2% in group B. Assume there are 100 people in each group. 16% of Group A would give you 16 people below 440, and 2% of group B would give you 2 people in Group B who scored below 440.

To find the fraction of students below 440 from B ====> Group B/(Total)

===> 2/(2+16)

Reduces to 1/9
GMAT Instructor
Joined: 24 Jun 2008
Posts: 967
Location: Toronto
Followers: 253

Kudos [?]: 653 [1] , given: 3

Re: normal distribution [#permalink]  09 Dec 2009, 02:30
1
KUDOS
There is no way to answer this question without consulting a stats table. Since that's impossible during a GMAT, it's not a realistic question. I know that the source gives an OA of B for this question, but that is the wrong answer. While you don't need to know this for the GMAT, when data is normally distributed, approximately 68.3% of values are within one standard deviation of the mean, and approximately 95.4% are within two standard deviations of the mean. If you round these values off to 68% and 95%, you'll get the answer given by the source. This rounding affects the answer, however; if you use exact values, you'll find that the correct answer to this question is closer to 1/8 than to 1/9. It's a very poorly designed question, and completely out of the scope of GMAT statistics, so it's best to ignore this question (and similar questions from the same source) and move on to better materials.
_________________

Nov 2011: After years of development, I am now making my advanced Quant books and high-level problem sets available for sale. Contact me at ianstewartgmat at gmail.com for details.

Private GMAT Tutor based in Toronto

VP
Status: There is always something new !!
Affiliations: PMI,QAI Global,eXampleCG
Joined: 08 May 2009
Posts: 1365
Followers: 11

Kudos [?]: 135 [0], given: 10

Re: normal distribution [#permalink]  17 May 2011, 23:39
got the concept now.

in A between 440-460 34% in b between 480-520 34%
in A between 420-440 14% in B between 440-480 14%

in A less than 420 2% in B less than 440 2%

hence (14+2) in A the percentage of people
and 2 in B the percentage of people having scores <440

thus ratio = 2/ (16+2) = 1/9 B
_________________

Visit -- http://www.sustainable-sphere.com/
Promote Green Business,Sustainable Living and Green Earth !!

Re: normal distribution   [#permalink] 17 May 2011, 23:39
Similar topics Replies Last post
Similar
Topics:
The average (arithmetic mean) of a normal distribution 1 15 Jul 2012, 15:36
Normal Distribution tutorial 0 29 May 2011, 04:56
Normal distribution 2 24 Mar 2011, 08:45
2 The average (arithmetic mean) of a normal distribution of a 11 16 Aug 2010, 10:25
1 Standard Normal Probability Distribution question 1 06 Jul 2010, 11:49
Display posts from previous: Sort by

normal distribution

 Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.