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

It is currently 23 Oct 2014, 05:16

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

2 employees are to be randomly chosen to form a committee

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Manager
Manager
avatar
Joined: 12 Feb 2012
Posts: 108
Followers: 1

Kudos [?]: 10 [0], given: 28

2 employees are to be randomly chosen to form a committee [#permalink] New post 21 Jul 2013, 13:11
There are 8 employees including Bob and Rachel. If 2 employees are to be randomly chosen to form a committee, what is the probability that the committee includes both Bob and Rachel?

Let B-Bob and R-Rachael
Using a reverse probability approach:

1) P(other than B&R)*P(other than B&R)=(6/8)(5/7)
2) P(B)*P(other than B&R)=(1/8)(6/7)
3) P(R)*P(other than B&R)=(1/8)(6/7)

(Let O-other) Situation 2) can happen in two ways BO or OB. Same thing with 3) RO or OR so we have to multiply 2) and 3) by 2!.

Hence the answer should be 1-[(6/8)(5/7)+2(1/8)(6/7)+2(1/8)(6/7)]. But this isn't the answer. What am I doing wrong?
Expert Post
Math Expert
User avatar
Joined: 02 Sep 2009
Posts: 23393
Followers: 3609

Kudos [?]: 28827 [0], given: 2852

Re: 2 employees are to be randomly chosen to form a committee [#permalink] New post 21 Jul 2013, 22:01
Expert's post
alphabeta1234 wrote:
There are 8 employees including Bob and Rachel. If 2 employees are to be randomly chosen to form a committee, what is the probability that the committee includes both Bob and Rachel?

Let B-Bob and R-Rachael
Using a reverse probability approach:

1) P(other than B&R)*P(other than B&R)=(6/8)(5/7)
2) P(B)*P(other than B&R)=(1/8)(6/7)
3) P(R)*P(other than B&R)=(1/8)(6/7)

(Let O-other) Situation 2) can happen in two ways BO or OB. Same thing with 3) RO or OR so we have to multiply 2) and 3) by 2!.

Hence the answer should be 1-[(6/8)(5/7)+2(1/8)(6/7)+2(1/8)(6/7)]. But this isn't the answer. What am I doing wrong?


Nothing is wrong.

The correct answer is \frac{1}{C^2_8}=\frac{1}{28} and 1-(\frac{6}{8}*\frac{5}{7}+2*\frac{1}{8}*\frac{6}{7}+2*\frac{1}{8}*\frac{6}{7}) is also equals to 1/28.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Re: 2 employees are to be randomly chosen to form a committee   [#permalink] 21 Jul 2013, 22:01
    Similar topics Author Replies Last post
Similar
Topics:
4 Experts publish their posts in the topic A committee of four is to be chosen from seven employees for JusTLucK04 7 21 Apr 2014, 05:07
2 Experts publish their posts in the topic Two MBA admissions committees are to be formed randomly fozzzy 2 24 Dec 2012, 06:49
3 Experts publish their posts in the topic A committee of 4 is to be chosen from 7 employees for a spec Professor5180 4 26 Jan 2012, 16:04
12 Experts publish their posts in the topic A committee of 3 has to be formed randomly from a group of 6 pmal04 11 18 Jul 2009, 13:03
A committee of 3 has to be formed randomly from a group of 6 MooseDrool 6 23 Aug 2007, 18:48
Display posts from previous: Sort by

2 employees are to be randomly chosen to form a committee

  Question banks Downloads My Bookmarks Reviews Important topics  


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®.