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.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Although for bunuel's extension of the original question, seems like he was using the binomial prob formula...m trials, n successes, prob of success p, prob of failure q ( or 1-p) B = mCn * p^n * q^(m-n) ......with m=5, n=3, p=q=1/2

Re: If a certain coin is flipped, the probability that the coin [#permalink]

Show Tags

03 Apr 2012, 20:43

whats the difference between this question and the following?

If the probability of rain on any given day in Chicago during the summer is 50%, independent of what happens on any other day, what is the probability of having exactly 3 rainy days from July 4 through July 8, inclusive?

is it because it could any 3 days between the 4th and 8th?

whats the difference between this question and the following?

If the probability of rain on any given day in Chicago during the summer is 50%, independent of what happens on any other day, what is the probability of having exactly 3 rainy days from July 4 through July 8, inclusive?

is it because it could any 3 days between the 4th and 8th?

The probability of rain each day is 1/2 and the probability of no rain is also 1/2. \(C^3_5=10\) represent ways to choose on which 3 days out of 5 there will be a rain, so \(P=C^3_5*(\frac{1}{2})^3*(\frac{1}{2})^2=\frac{10}{32}=\frac{5}{16}\).

Or think about it this way: we want the probability of the following event: RRRNN, where R represent rain day and N represents no-rain day. Now, each R and each N have individual probability of 1/2, so \((\frac{1}{2})^5\).

But the case of RRRNN can occur in many ways: RRRNN, RRNRRN, RNRRN, NRRRN, ... basically it will be equla to # of arrangements (permutations) of 5 letters RRRNN out of which there are 3 identical R's and 2 identical N's. That # of arrangements is \(\frac{5!}{3!2!}\), (notice that it's the same as \(C^3_5\)). So, finally \(P=\frac{5!}{3!2!}*(\frac{1}{2})^5=\frac{5}{16}\).

Re: If a certain coin is flipped, the probability that the coin [#permalink]

Show Tags

10 Jul 2013, 08:54

My try ( I am a beginner trying to solve this kind of problems using combinations

\(\frac{C^5_3}{{(C^2_1)^5}}\) = 1/32

\(C^5_3\) : number of combinations in which we obtain 3 H in 5 tosses

\((C^2_1)^5\) : number of combinations of T or H in 5 tosses
_________________

Encourage cooperation! If this post was very useful, kudos are welcome "It is our attitude at the beginning of a difficult task which, more than anything else, will affect It's successful outcome" William James

Re: If a certain coin is flipped, the probability that the coin [#permalink]

Show Tags

06 Mar 2015, 19:26

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.
_________________

Re: If a certain coin is flipped, the probability that the coin [#permalink]

Show Tags

06 Mar 2016, 09:30

Bunuel wrote:

marcodonzelli wrote:

If a certain coin is flipped, the probability that the coin will land heads is 1/2. If the coin is flipped 5 times, what is the probability that it will land heads up on the first 3 flips and not on the last 2 flips?

A. 3/5 B. 1/2 C. 1/5 D. 1/8 E. 1/32

We want the probability that coin will land heads up on the first 3 flips and not on the last 2 flips. So there is ONLY one favorable outcome, namely heads up on the first 3 flips and tails up on the last 2 flips: HHHTT.

# of total out comes is 2^5=32.

P=favorable/total=1/32.

Answer: E.

In this problem is the above the equivalent of some of these other answers (and how I approached the problem) of simply doing

Chance for tails & chance for heads both = 1/2

Chance of heads 1/2 * chance of heads *chance of heads 1/2 * chance of heads 1/2 * chance of tails 1/2 * chance of tails 1/2?

I see the above total as 2^5 over 1 possibility so the numbers are the same but for straight forward problems such as this one is the listed 1/2*1/2*1/2 an acceptable approach or just a coincidence it works for this problem?
_________________

Re: If a certain coin is flipped, the probability that the coin will land [#permalink]

Show Tags

06 Jan 2017, 22:07

This question is simple since the coin is ideal(i.e., 0.5 probability for either event) The question asks us to find the probability of the occurrence of the event HHHTT This is just the product, P(H)*P(H)*P(H)*P(T)*P(T)=(0.5)*(0.5)*(0.5)*(0.5)*(0.5) =1/32 If the coin was skewed,i.e., say probability of landing head is 0.75,then the answer would have been, P(H)*P(H)*P(H)*P(T)*P(T)=(0.75)*(0.75)*(0.75)*(0.25)*(0.25) =27/1024
_________________

------------------------ Anjan Surepeddi IIT Kharagpur India

gmatclubot

Re: If a certain coin is flipped, the probability that the coin will land
[#permalink]
06 Jan 2017, 22:07

Happy New Year everyone! Before I get started on this post, and well, restarted on this blog in general, I wanted to mention something. For the past several months...

It’s quickly approaching two years since I last wrote anything on this blog. A lot has happened since then. When I last posted, I had just gotten back from...

Post-MBA I became very intrigued by how senior leaders navigated their career progression. It was also at this time that I realized I learned nothing about this during my...