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

It is currently 30 Sep 2014, 10:43

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

A group of friends have decided to take a roadtrip. Whenever

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Current Student
User avatar
Joined: 29 Jan 2005
Posts: 5252
Followers: 23

Kudos [?]: 134 [0], given: 0

Reviews Badge
A group of friends have decided to take a roadtrip. Whenever [#permalink] New post 01 Oct 2005, 20:39
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
A group of friends have decided to take a roadtrip. Whenever they come to a fork in the road, they will flip a fair coin to decide whether to head right or left. If the coin is heads, they will head right. If the coin is tails, they will head left. If the friends have made seven decisions, what is the probability that they took exactly four lefts?

A. 1/16
B. 1/32
C. 21/25
D. 35/128
E. 4/7
Manager
Manager
avatar
Joined: 15 Jul 2005
Posts: 106
Followers: 1

Kudos [?]: 4 [0], given: 0

 [#permalink] New post 01 Oct 2005, 23:21
d) 35/128

7C4*(1/2)^4*(1/2)^3 = 35/(16*8)=35/128
VP
VP
User avatar
Joined: 13 Jun 2004
Posts: 1128
Location: London, UK
Schools: Tuck'08
Followers: 6

Kudos [?]: 24 [0], given: 0

 [#permalink] New post 02 Oct 2005, 03:18
D too
I used bernoulli method too as chets did
Current Student
User avatar
Joined: 29 Jan 2005
Posts: 5252
Followers: 23

Kudos [?]: 134 [0], given: 0

Reviews Badge
 [#permalink] New post 02 Oct 2005, 03:27
OA is D.

Antmavel, could you please explain the bernoulli method?? :oops:
Senior Manager
Senior Manager
avatar
Joined: 30 Oct 2004
Posts: 289
Followers: 1

Kudos [?]: 8 [0], given: 0

 [#permalink] New post 02 Oct 2005, 05:08
D) Same method ... applying the formula nCr*(p^r)*(q^(n-r))

When to apply Bernoulli's trials....
1) Only two possible outcomes for each trial (Yes or No, Heads or Tail, or simply p=Success & q= Failure. Note: p need not be same as q)
2) The probability of success (p) is same for each trial
3) Trials are independent (n is independent)

So in this problem, there are seven trials and you want to find the probability of success for exactly 4 of them.
For 1 trial Success is: p= 1/2 (its either Yes or No)
q = 1-p = 1/2
n =7
r=4
Applying BT, you get 35/128.

Added: I also found the following link on this website (see Appendix A) http://www.gmatclub.com/content/courses/quantitative/probability.php
_________________

-Vikram

VP
VP
User avatar
Joined: 13 Jun 2004
Posts: 1128
Location: London, UK
Schools: Tuck'08
Followers: 6

Kudos [?]: 24 [0], given: 0

 [#permalink] New post 02 Oct 2005, 19:36
GMATT73 wrote:
OA is D.

Antmavel, could you please explain the bernoulli method?? :oops:


vikramm, your post was perfect :) Nice explanation
  [#permalink] 02 Oct 2005, 19:36
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic PE Takes a Roadtrip (and so should you) JonAdmissionado 0 29 May 2011, 07:51
Help me decide friends... samidh 0 16 Sep 2010, 22:10
Help me decide friends... samidh 0 16 Sep 2010, 21:37
A group of six friends (A, B, C, D, E and F) plans on taking andrehaui 5 20 Jun 2007, 12:02
A group of six friends (A, B, C, D, E and F) plans on taking andrehaui 3 30 May 2007, 13:19
Display posts from previous: Sort by

A group of friends have decided to take a roadtrip. Whenever

  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®.