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

It is currently 29 Aug 2014, 04:14

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

probability question - coin toss

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
avatar
Joined: 16 Jul 2006
Posts: 14
Location: New Orleans
Followers: 0

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

probability question - coin toss [#permalink] New post 25 Aug 2006, 16:19
Hey there. I sit for the GMATic on Tuesday. I am generally pretty strong on probability, but these type of coin toss questions occassionally trip me up:

A coin is tossed four times. How many ways can you get exactly two heads?



Any suggestions on how to best conceptualize this type of question (as well as how you arrived at the answer) would be greatly appreciated.
Kaplan Promo CodeKnewton GMAT Discount CodesVeritas Prep GMAT Discount Codes
1 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 14 Jul 2005
Posts: 405
Followers: 1

Kudos [?]: 6 [1] , given: 0

GMAT Tests User
 [#permalink] New post 25 Aug 2006, 16:45
1
This post received
KUDOS
Total outcomes = 2*2*2*2 = 16

Now for 2 heads these are the possibilities

HHTT
THHT
TTHH
HTTH
THTH
HTHT

i.e. 6

Hence answer
= no. of favourable outcomoes/total no. of outcomes
= 6/16
= 3/8
Intern
Intern
avatar
Joined: 17 Apr 2006
Posts: 42
Followers: 0

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

Re: probability question - coin toss [#permalink] New post 25 Aug 2006, 19:14
pws wrote:
Hey there. I sit for the GMATic on Tuesday. I am generally pretty strong on probability, but these type of coin toss questions occassionally trip me up:

A coin is tossed four times. How many ways can you get exactly two heads?



Any suggestions on how to best conceptualize this type of question (as well as how you arrived at the answer) would be greatly appreciated.


Such problems can be easily solved by using the binomial formula. For calculating probability of "r" outcomes in an experiment with n-trials, the formula states that:
P = C(n,r) (p^r ) (q^(n-r))

where p is the probability of getting 1 outcome succesful, and q is the probability of getting that same outcome as a failure.

In this case, p = 1/2 , the probability of getting a head in a given coin toss. q = 1/2 as there is no other outcome aside from tail.

Thus: P = C(4.2) (0.5)^2 * (0.5)^2
= 3 (0.25)(0.25) = 3/8
Intern
Intern
avatar
Joined: 13 May 2006
Posts: 21
Followers: 0

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

Re: probability question - coin toss [#permalink] New post 25 Aug 2006, 19:24
pws wrote:
Hey there. I sit for the GMATic on Tuesday. I am generally pretty strong on probability, but these type of coin toss questions occassionally trip me up:

A coin is tossed four times. How many ways can you get exactly two heads?



Any suggestions on how to best conceptualize this type of question (as well as how you arrived at the answer) would be greatly appreciated.


Use binomial distribution, when the possible favourable/nonfavourable events are fixed 3/8
Director
Director
User avatar
Joined: 28 Dec 2005
Posts: 761
Followers: 1

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

GMAT Tests User
 [#permalink] New post 26 Aug 2006, 06:23
Agree that the binomial distribution is the way to go here:

P = nCr X p^r X q^(n-r)

will give the probability. However, this does not give us the actual number of ways for getting 2H and 2T. To get that we multiply the probability by the total number of outcomes.

Hence we get 6/16 X 2^4 = 6
Manager
Manager
User avatar
Joined: 23 Jul 2006
Posts: 50
Followers: 1

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

 [#permalink] New post 26 Aug 2006, 14:30
HI guys....

I have a question

How many ways can you get exactly two heads? => this question means to calculate probability?

or means 4P2?

I will really appreciate your answers---
_________________

Woody crack the GMAT

Senior Manager
Senior Manager
avatar
Joined: 14 Aug 2006
Posts: 368
Followers: 1

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

GMAT Tests User
 [#permalink] New post 26 Aug 2006, 20:50
zorro 13 has raised an interesting question..

How do we know if it is the probability or if it literally means the number of ways 4C2 that you could get exactly two heads?

I think the answer choices should give a clue.
Director
Director
User avatar
Joined: 28 Dec 2005
Posts: 761
Followers: 1

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

GMAT Tests User
 [#permalink] New post 26 Aug 2006, 21:47
Read my answer again. The question asks for the number of ways. Once you know the probability (which is easier to calculate in this case), you can multiply it by the total number of possibilities to get the needed answer. Does this help?
Senior Manager
Senior Manager
avatar
Joined: 14 Aug 2006
Posts: 368
Followers: 1

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

GMAT Tests User
 [#permalink] New post 26 Aug 2006, 21:52
yep, in this case, it is the number of ways not the probability
Manager
Manager
User avatar
Joined: 23 Jul 2006
Posts: 50
Followers: 1

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

 [#permalink] New post 26 Aug 2006, 23:27
Thank you guys.....

.
_________________

Woody crack the GMAT

  [#permalink] 26 Aug 2006, 23:27
    Similar topics Author Replies Last post
Similar
Topics:
1 Probability ... tossing coins Sepideh2612 8 07 Nov 2011, 05:15
2 Coin Tossing-Probability soaringAlone 1 15 Jun 2011, 21:33
For one toss of a certain coin the probability that the samuliakin 1 04 Sep 2007, 23:29
For one toss of a certain coin, the probability that the john2005 7 22 May 2006, 14:13
For one toss of a certain coin, the probability that the zoom 4 10 Sep 2005, 12:54
Display posts from previous: Sort by

probability question - coin toss

  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®.