Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 24 May 2017, 02:08

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# A drawer contains 36 socks, and 2 socks are selected at

Author Message
TAGS:

### Hide Tags

Director
Joined: 01 Apr 2008
Posts: 882
Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014
Followers: 30

Kudos [?]: 704 [3] , given: 18

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

### Show Tags

25 Oct 2009, 05:13
3
KUDOS
6
This post was
BOOKMARKED
00:00

Difficulty:

55% (hard)

Question Stats:

49% (01:45) correct 51% (00:52) wrong based on 517 sessions

### HideShow timer Statistics

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.
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Sep 2009
Posts: 38850
Followers: 7721

Kudos [?]: 105956 [6] , given: 11602

### Show Tags

25 Oct 2009, 17:08
6
KUDOS
Expert's post
Economist wrote:
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.

_________________
Director
Joined: 13 Nov 2003
Posts: 789
Location: BULGARIA
Followers: 1

Kudos [?]: 52 [0], given: 0

### Show Tags

26 Oct 2009, 05:15
Hi,
Think that the ans is E
It is not mentioned that the socks are only B&W
Regards
Math Expert
Joined: 02 Sep 2009
Posts: 38850
Followers: 7721

Kudos [?]: 105956 [1] , given: 11602

### Show Tags

26 Oct 2009, 08:26
1
KUDOS
Expert's post
BG wrote:
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.

_________________
Intern
Joined: 27 Feb 2012
Posts: 2
Followers: 0

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

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

### Show Tags

21 Mar 2012, 12:43
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 !)
Intern
Joined: 21 Mar 2012
Posts: 5
Followers: 0

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

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

### Show Tags

21 Mar 2012, 12:56
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.

IMO : A
Senior Manager
Joined: 19 Oct 2010
Posts: 262
Location: India
GMAT 1: 560 Q36 V31
GPA: 3
Followers: 7

Kudos [?]: 80 [0], given: 27

### Show Tags

01 Jul 2012, 08:44
Bunuel wrote:
Economist wrote:
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.

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

petrifiedbutstanding

Math Expert
Joined: 02 Sep 2009
Posts: 38850
Followers: 7721

Kudos [?]: 105956 [0], given: 11602

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

### Show Tags

07 Jun 2013, 06:12
Bumping for review and further discussion*. Get a kudos point for an alternative solution!

*New project from GMAT Club!!! Check HERE

Theory on probability problems: math-probability-87244.html

All DS probability problems to practice: search.php?search_id=tag&tag_id=33
All PS probability problems to practice: search.php?search_id=tag&tag_id=54

Tough probability questions: hardest-area-questions-probability-and-combinations-101361.html

_________________
Manager
Joined: 27 Apr 2012
Posts: 62
Location: United States
GMAT Date: 06-11-2013
GPA: 3.5
WE: Marketing (Consumer Products)
Followers: 1

Kudos [?]: 57 [1] , given: 21

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

### Show Tags

09 Jun 2013, 02:41
1
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.

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 15413
Followers: 649

Kudos [?]: 206 [0], given: 0

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

### Show Tags

25 Jun 2014, 05:02
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.
_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 15413
Followers: 649

Kudos [?]: 206 [0], given: 0

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

### Show Tags

13 Nov 2015, 01:07
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.
_________________
Re: A drawer contains 36 socks, and 2 socks are selected at   [#permalink] 13 Nov 2015, 01:07
Similar topics Replies Last post
Similar
Topics:
1 A drawer contains 12 socks, of which 8 are black and 4 are white. If 3 2 17 May 2017, 04:45
3 A drawer contains 6 socks. If two socks are randomly 2 16 Nov 2016, 03:40
1 Two socks are to be picked at random from a drawer containing only bla 2 04 Aug 2016, 07:31
7 If a pencil is selected at random from a desk drawer, what 9 10 Apr 2017, 09:30
45 A drawer contains 8 socks, and 2 socks are selected at 11 13 Sep 2016, 05:11
Display posts from previous: Sort by