Denette tosses two coins. What is the probability that she has tossed 2 heads, given that she has tossed at least 1 head?
a)1/3
b)1/4
c)4/3
d)3/4
e)1/2
a
conditional probability
This topic has expert replies
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Here's a non-formulaic approach.sana.noor wrote:Denette tosses two coins. What is the probability that she has tossed 2 heads, given that she has tossed at least 1 head?
a)1/3
b)1/4
c)4/3
d)3/4
e)1/2
a
I'll assume that the probability of tossing heads = the probability of tossing tails = 0.5
Since each outcome is equally likely, let's draw a tree diagram to see all of the possible outcomes:
So, there are 4 possible outcomes and each outcome is equally likely.
The 4 outcomes are HH, HT, TH and TT
Now it's given that there's at least one head.
So, of the 4 possible outcomes, only 3 of them are such that there's at least one head.
Now that we know we've narrowed the field to three equally-likely outcomes (HH, HT and TH), we want the probability of HH
The probability is [spoiler]1/3 (answer = A)[/spoiler]
Cheers,
Brent
-
- Legendary Member
- Posts: 512
- Joined: Mon Jun 18, 2012 11:31 pm
- Thanked: 42 times
- Followed by:20 members
Brent should one practice Binomal theorem to find the probability? is it important to study for gmat or one can skip?
Work hard in Silence, Let Success make the noise.
If you found my Post really helpful, then don't forget to click the Thank/follow me button.
If you found my Post really helpful, then don't forget to click the Thank/follow me button.
GMAT/MBA Expert
- Brent@GMATPrepNow
- GMAT Instructor
- Posts: 16207
- Joined: Mon Dec 08, 2008 6:26 pm
- Location: Vancouver, BC
- Thanked: 5254 times
- Followed by:1268 members
- GMAT Score:770
Well, you could use the binomial theorem for some questions, but the GMAT would never ask you a question that requires it.
I'd skip it.
Cheers,
Brent
I'd skip it.
Cheers,
Brent
- GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
Here are all of ways to get at least one heads:sana.noor wrote:Denette tosses two coins. What is the probability that she has tossed 2 heads, given that she has tossed at least 1 head?
a)1/3
b)1/4
c)4/3
d)3/4
e)1/2
a
HT
HH
TH
Of these 3 options, one the outcome in red is favorable, implying that the probability = 1/3.
The correct answer is A.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
GMAT/MBA Expert
- Anurag@Gurome
- GMAT Instructor
- Posts: 3835
- Joined: Fri Apr 02, 2010 10:00 pm
- Location: Milpitas, CA
- Thanked: 1854 times
- Followed by:523 members
- GMAT Score:770
Number of outcomes with at least one head = 3 {HH, TH, HT}sana.noor wrote:Denette tosses two coins. What is the probability that she has tossed 2 heads, given that she has tossed at least 1 head?
Number of outcomes with two heads = 1 {HH}
Hence, required probability = 1/3
The correct answer is A.
Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)
Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/