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

It is currently 26 May 2016, 03:51
GMAT Club Tests

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

John throws a coin until a series of three consecutive heads

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Intern
Intern
avatar
Joined: 24 Nov 2012
Posts: 3
Followers: 0

Kudos [?]: 2 [0], given: 13

John throws a coin until a series of three consecutive heads [#permalink]

Show Tags

New post 11 Dec 2012, 12:59
2
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

59% (01:48) correct 41% (01:09) wrong based on 73 sessions

HideShow timer Statistics

John throws a coin until a series of three consecutive heads or three consecutive tails appears. What is the probability that the game will end after the fourth throw?

(A) 1/16
(B) 2/16
(C) 3/16
(D) 7/16
(E) 9/16
[Reveal] Spoiler: OA
Expert Post
2 KUDOS received
Magoosh GMAT Instructor
User avatar
Joined: 28 Dec 2011
Posts: 3062
Followers: 1023

Kudos [?]: 4432 [2] , given: 48

Re: probability problem. has anybody the explanation for it [#permalink]

Show Tags

New post 11 Dec 2012, 13:09
2
This post received
KUDOS
Expert's post
david1983 wrote:
John throws a coin until a series of three consecutive heads or three consecutive tails appears. What is the probability that the game will end after the fourth throw?
(A) 1/16
(B) 2/16
(C) 3/16
(D) 7/16
(E) 9/16

Great question! I'm happy to help. :-)

Let's consider the routes that would lead to ending the game on the fourth toss. In order to be a win at that point, tosses #2 & #3 & #4 would all have to be the same, either H or T, and in order for the game NOT to end on the third toss, the first toss would have to be different from the other four. Thus, the only two possible sequences are

H-T-T-T ----> P = (1/2)^4 = 1/16

T-H-H-H ----> P = (1/2)^4 = 1/16

Either one of these would satisfy the condition, so we could have one or the other. OR means add in probability.

1/16 + 1/16 = 2/16 = 1/8

Answer (B). Incidentally, the GMAT would NEVER give the unsimplified fraction 2/16 --- it would always give the simplified form 1/8.

Does all this make sense?

Mike :-)
_________________

Mike McGarry
Magoosh Test Prep

Image

Image

1 KUDOS received
GMAT Club Legend
GMAT Club Legend
User avatar
Joined: 09 Sep 2013
Posts: 9630
Followers: 465

Kudos [?]: 120 [1] , given: 0

Premium Member
Re: John throws a coin until a series of three consecutive heads [#permalink]

Show Tags

New post 06 Aug 2015, 01:31
1
This post received
KUDOS
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

Re: John throws a coin until a series of three consecutive heads   [#permalink] 06 Aug 2015, 01:31
    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic John received a 10% raise each month for three consecutive months. Wha Bunuel 2 10 Jan 2016, 08:27
1 Experts publish their posts in the topic John flips a coin 4 times. What is the probability that he gets heads tiamo2015 5 28 Dec 2014, 19:11
3 Experts publish their posts in the topic On three consecutive flips of a coin, what is the probabilit josemnz83 4 09 Jul 2013, 14:44
13 Experts publish their posts in the topic A man alternately tosses a coin and throws a die beginning pradhan 10 25 Dec 2009, 23:34
9 Experts publish their posts in the topic Marco and Maria toss a coin three times. Each time a head is marcodonzelli 14 14 Jan 2008, 05:57
Display posts from previous: Sort by

John throws a coin until a series of three consecutive heads

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| 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®.