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:

(2) W=B+4, as we don't know whether drawer contains only white and black socks, or there are also some other color socks, we can not determine the # of B. not sufficient.

Hi, Think that the ans is E It is not mentioned that the socks are only B&W Regards

You are right, it's not mentioned and that is why (2) is not sufficient. But for (1): saying that the probability of drawing the FIRST black sock is 4/9 means that we have 4 chance out of 9 to have black OR as there are total of 36 socks, 16 chances out of 36. That's clearly gives us the NUMBER OF BLACK SOCKS in the drawer, even though we still don't know the number and colors of the other socks (well, there are total 36-16=20 others but we don't know their color). So (1) is still sufficient to determine the probability that both socks are black 4/9*15/35=4/21.

Re: A drawer contains 36 socks, and 2 socks are selected at [#permalink]

Show Tags

21 Mar 2012, 11:43

I think it's D: (1) is obvious (2) The number of white socks in the drawer is 4 more than the number of black socks. Let’s B be the number of black socks and W the number of white. W = B +4 and we know 36 = B +W then W = 36 – B = B + 4 => 2B = 32 => B =16 (Sufficient !)

Re: A drawer contains 36 socks, and 2 socks are selected at [#permalink]

Show Tags

21 Mar 2012, 11:56

FoudMine wrote:

I think it's D: (1) is obvious (2) The number of white socks in the drawer is 4 more than the number of black socks. Let’s B be the number of black socks and W the number of white. W = B +4 and we know 36 = B +W then W = 36 – B = B + 4 => 2B = 32 => B =16 (Sufficient !)

But you are wrongfully assuming from the question that there are only B and W socks, which is not necessarily the case.

A drawer contains 36 socks, and 2 socks are selected at random without replacement. What is the probability that both socks are black?

(1) The probability is 4/9 that the first sock is black.

(2) The number of white socks in the drawer is 4 more than the number of black socks.

Total # of socks 36.

(1) P(B)=4/9 --> B=16 --> P(BB)=16/36*15/35=4/21. Sufficient. (2) W=B+4, as we don't know whether drawer contains only white and black socks, or there are also some other color socks, we can not determine the # of B. not sufficient.

Answer: A.

This was how I analyzed it! And if I'm doing what you're doing, I'm finally getting somewhere..
_________________

Re: A drawer contains 36 socks, and 2 socks are selected at [#permalink]

Show Tags

09 Jun 2013, 01:41

1

This post received KUDOS

Let the number of black socks = b

So the question can be rephrased as b/36 * (b-1)/35 = ?

Stmt 1 : The probability of the 1st sock being black = b/36 = 4/9

Cross multiply and you get b = 16

Hence we know that the 16 is the total number of black socks

This information helps us calculate the exact probability of getting 2 black socks. Hence stmt 1 is sufficient.

Stmt 2 : Let the number of white socks be w hence, w = b+4

This information does not help us arrive at the exact probability of getting 2 black socks because we are not told whether the 36 socks consist of only black and white socks or whether there are more colours as well.

Since we can not derive exact information,this statement is insufficient.

Re: A drawer contains 36 socks, and 2 socks are selected at [#permalink]

Show Tags

25 Jun 2014, 04:02

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: A drawer contains 36 socks, and 2 socks are selected at [#permalink]

Show Tags

13 Nov 2015, 00:07

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.
_________________

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...

Happy 2017! Here is another update, 7 months later. With this pace I might add only one more post before the end of the GSB! However, I promised that...