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

It is currently 28 Aug 2014, 19:21

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

hard probability problem

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
avatar
Joined: 18 Jul 2009
Posts: 54
Followers: 2

Kudos [?]: 38 [0], given: 7

hard probability problem [#permalink] New post 26 Nov 2009, 12:45
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

75% (06:16) correct 25% (38:14) wrong based on 5 sessions
Kurt, a painter, has 9 jars of paint 4 of which are yellow, 2 are red and the remaining jars are brown. Kurt will combine 3 jars of paint into a new container to make a new color which he will name according to the following conditions:

Brun Y if the paint contains 2 jars of brown paint and no yellow
Brun X if the paint contains 3 jars of brown paint
Jaune X if the paint contains at least 2 jars of yellow
Jaune Y if the paint contains exactly 1 jar of yellow

What is the probability that the new color will be jaune?

A) 5/42
B) 37/42
C) 1/21
D) 4/9
E)5/9

I am getting

jaune x+jaune y

4/9*5/8*4/7 +( 4/9*3/8*5/7 + 4/9*3/8*2/7)

= 41/126

I know if i use other method i.e (1-probability of no yellow) then answer is


1-5/9*4/8*3/7 = 1-5/42=37/42

Can someone tell me where I am going wrong in 1st method
Expert Post
1 KUDOS received
CEO
CEO
User avatar
Joined: 17 Nov 2007
Posts: 3571
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 357

Kudos [?]: 1753 [1] , given: 358

GMAT ToolKit User GMAT Tests User Premium Member
Re: hard probability problem [#permalink] New post 26 Nov 2009, 13:22
1
This post received
KUDOS
Expert's post
3 * 4/9*5/8*4/7 +( 3 * 4/9*3/8*5/7 + 4/9*3/8*2/7) = (3*4*5*4 + 3*4*3*5 + 4*3*2)/(9*8*7) = (4*5+3*5+2)/(3*2*7) = 37/42

In other words, you forgot that besides y?? there are two other ways: ?y? and ??y. The same in the case of yy?.
_________________

HOT! GMAT TOOLKIT 2 (iOS) / GMAT TOOLKIT (Android) - The OFFICIAL GMAT CLUB PREP APP, a must-have app especially if you aim at 700+ | PrepGame

Manager
Manager
avatar
Joined: 18 Jul 2009
Posts: 54
Followers: 2

Kudos [?]: 38 [0], given: 7

Re: hard probability problem [#permalink] New post 26 Nov 2009, 13:37
Thanks walker.

+1 for you
Intern
Intern
avatar
Joined: 31 Mar 2010
Posts: 17
Schools: Stanford GSB (waiting), Wharton (wl w/ int), INSEAD (admit)
WE 1: Top-Tier MC
Followers: 0

Kudos [?]: 3 [0], given: 12

Re: hard probability problem [#permalink] New post 31 Mar 2010, 08:04
Any yellow paint in the mix results in a jaune paint once combined.

So, probability of jaune paint is (1 - probability of all combinations that do not contain any yellow)

# of combinations = 9C3 = 84 {9 pots, choose 3}
# of combinations that do not contain any yellow = 5C3 = 10 {5 non-yellow pots, choose 3}
So, probability of combinations that DO NOT contain any yellow 10/84

So, probability of combinations that DO contain yellow = 1 - 10/84 = 74/84 = 37/42


Nick

Edit: Spelling and clarity
Re: hard probability problem   [#permalink] 31 Mar 2010, 08:04
    Similar topics Author Replies Last post
Similar
Topics:
1 1 hard probability dimri10 2 13 Jun 2011, 11:24
1 Hard probability gmat1220 4 02 Mar 2011, 18:16
1 Experts publish their posts in the topic Hard probability problem: 2 dice sum of 3 BEFORE sum of 7 catennacio 9 06 Oct 2010, 00:21
2 Hard probability question chipmo 10 01 Jul 2008, 22:17
HARD DS speed problem danielwaugh 12 01 Oct 2007, 21:35
Display posts from previous: Sort by

hard probability problem

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.