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:

well, they do present some "trick" questions. for ex, in case of a DS question, involving a few variables like a<x<b, etc, everything would look easy except that it wouldn't have mentioned that x is an integer (i hope you get the example). so how is tht different from this? where do we draw the line?

Whenever you see a DS question you may expect the answer to be in form of a value or yes/no.

In the mentioned question, using (1), even if the coin is fair, we can only predict that probability of heads is 1/2 or 5 out of 10 turns. but, the value (1/2) is practically based on large number of coin flips. It may happen that first 10 flips result in to 10 heads or no heads at all.

Thus, (1) is insufficient. (differentiating between the probability and actual results)

Using (2), we get a straight forward answer: heads = 5/8 N so 5/8 of flips were heads.

Whenever you see a DS question you may expect the answer to be in form of a value or yes/no.

In the mentioned question, using (1), even if the coin is fair, we can only predict that probability of heads is 1/2 or 5 out of 10 turns. but, the value (1/2) is practically based on large number of coin flips. It may happen that first 10 flips result in to 10 heads or no heads at all.

Thus, (1) is insufficient. (differentiating between the probability and actual results)

Using (2), we get a straight forward answer: heads = 5/8 N so 5/8 of flips were heads.

Thus, answer is (B)

Regards,

That doesn't exactly answer my question. I know how to solve it, however, the assumption is the coin is fair. If that's not given, then E should be the answer.

In GMAT, you don't need to take any assumption in DS question. In a particular info is required it would be mentioned. Now in this question it doesn't matter whether the coin is unfair, since the choices don't require this assumption.

in (1), we can never tell about no. of heads, in (2), 3/8N are tails so other 5/8 should be heads.

Let me know if this is helpful.

Regards,

synecdoche wrote:

cyberjadugar wrote:

Hi,

Whenever you see a DS question you may expect the answer to be in form of a value or yes/no.

In the mentioned question, using (1), even if the coin is fair, we can only predict that probability of heads is 1/2 or 5 out of 10 turns. but, the value (1/2) is practically based on large number of coin flips. It may happen that first 10 flips result in to 10 heads or no heads at all.

Thus, (1) is insufficient. (differentiating between the probability and actual results)

Using (2), we get a straight forward answer: heads = 5/8 N so 5/8 of flips were heads.

Thus, answer is (B)

Regards,

That doesn't exactly answer my question. I know how to solve it, however, the assumption is the coin is fair. If that's not given, then E should be the answer.

"X flipped a coin N times. What fraction of the flips came up heads? (1) N=10 (2) 3/8N came up tails. "

Do you just answer B or do you try to be extra smart and ask whether it's a fair coin? (And hence, answer E)

The GMAT will always make clear whether the coin is fair or not (for example it can be given that the probability of heads is 0.4 and the probability of tails is 0.6). So, you shouldn't worry about that issue.

Having said that, Kaplan also makes it clear in the original question, which is: Susan flipped a fair coin N times. What fraction of the flips came up heads? (1) N = 24 (2) The number of flips that came up tails was 3/8*N

Clearly, the first statement is not sufficient. Even though expected number of heads is 12 out of 24 but we don't know how many heads there were actually.

As for the second statement: since 3/8 of the flips came up tails then the remaining 5/8 of the flips must have been heads (provided N>0).

"X flipped a coin N times. What fraction of the flips came up heads? (1) N=10 (2) 3/8N came up tails. "

Do you just answer B or do you try to be extra smart and ask whether it's a fair coin? (And hence, answer E)

The GMAT will always make clear whether the coin is fair or not (for example it can be given that the probability of heads is 0.4 and the probability of tails is 0.6). So, you shouldn't worry about that issue.

Having said that, Kaplan also makes it clear in the original question, which is: Susan flipped a fair coin N times. What fraction of the flips came up heads? (1) N = 24 (2) The number of flips that came up tails was 3/8*N

Clearly, the first statement is not sufficient. Even though expected number of heads is 12 out of 24 but we don't know how many heads there were actually.

As for the second statement: since 3/8 of the flips came up tails then the remaining 5/8 of the flips must have been heads (provided N>0).

Hope it's clear.

Nice explanation Bunuel, if we assume that this is real GMAT question, and there is no indication that n>0 or it does not equal to 0, should we pick C as answer?
_________________

If you found my post useful and/or interesting - you are welcome to give kudos!

"X flipped a coin N times. What fraction of the flips came up heads? (1) N=10 (2) 3/8N came up tails. "

Do you just answer B or do you try to be extra smart and ask whether it's a fair coin? (And hence, answer E)

The GMAT will always make clear whether the coin is fair or not (for example it can be given that the probability of heads is 0.4 and the probability of tails is 0.6). So, you shouldn't worry about that issue.

Having said that, Kaplan also makes it clear in the original question, which is: Susan flipped a fair coin N times. What fraction of the flips came up heads? (1) N = 24 (2) The number of flips that came up tails was 3/8*N

Clearly, the first statement is not sufficient. Even though expected number of heads is 12 out of 24 but we don't know how many heads there were actually.

As for the second statement: since 3/8 of the flips came up tails then the remaining 5/8 of the flips must have been heads (provided N>0).

Hope it's clear.

Nice explanation Bunuel, if we assume that this is real GMAT question, and there is no indication that n>0 or it does not equal to 0, should we pick C as answer?

Even though it's quite natural to assume that N must be more than zero, the real question would state it somehow to eliminate this ambiguity.
_________________

Re: Susan flipped a fair coin N times. What fraction of the [#permalink]

Show Tags

25 Jan 2016, 04:57

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: Susan flipped a fair coin N times. What fraction of the [#permalink]

Show Tags

05 Aug 2016, 06:03

Suson flipped a fair coin N times. What fraction of the flips came up heads?

(1) N = 24 SO close yet so far. Because we know that the coin is a fair therefore the probability of getting heads is 50 % but probability does not mean "Definitely".

Since the question is asking "FRACTION" of HEAD which is \(\frac{# of HEAD}{# of TOTAL FLIPS}\).

we cannot get this value because we dont know how many times the coin actually came as HEAD. All we know that its probability of gettting a head was 50% in each of the 24 tosses but how many times it was actually head is not known

INSUFFICIENT

(2) The number of flips that came up tails was 3/8*N

Number of times that tail came up = \(\frac{3N}{8}\)

Therefore total number of times head came up = \(\frac{5N}{8}\)

Fraction of head = \(\frac{5N}{8}*\frac{1}{N} =\frac{5}{8}\)of total

SUFFICIENT

ANSWER IS B
_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly. FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.

gmatclubot

Re: Susan flipped a fair coin N times. What fraction of the
[#permalink]
05 Aug 2016, 06:03

Military MBA Acceptance Rate Analysis Transitioning from the military to MBA is a fairly popular path to follow. A little over 4% of MBA applications come from military veterans...

Best Schools for Young MBA Applicants Deciding when to start applying to business school can be a challenge. Salary increases dramatically after an MBA, but schools tend to prefer...

Marty Cagan is founding partner of the Silicon Valley Product Group, a consulting firm that helps companies with their product strategy. Prior to that he held product roles at...