A jar contains 4 black and 3 white balls. If you pick two ba : GMAT Problem Solving (PS)
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 16 Jan 2017, 14:57

### 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 jar contains 4 black and 3 white balls. If you pick two ba

Author Message
TAGS:

### Hide Tags

BSchool Forum Moderator
Joined: 27 Aug 2012
Posts: 1196
Followers: 129

Kudos [?]: 1457 [0], given: 142

A jar contains 4 black and 3 white balls. If you pick two ba [#permalink]

### Show Tags

30 Aug 2013, 05:09
2
This post was
BOOKMARKED
00:00

Difficulty:

45% (medium)

Question Stats:

64% (01:54) correct 36% (01:29) wrong based on 138 sessions

### HideShow timer Statistics

A jar contains 4 black and 3 white balls. If you pick two balls at the same time, what's the probability that one ball is black and one is white?

A. 2/7
B. 5/7
C. 4/7
D. 3/7
E. 1/2
[Reveal] Spoiler: OA

_________________

Last edited by bagdbmba on 30 Aug 2013, 05:45, edited 1 time in total.
Math Expert
Joined: 02 Sep 2009
Posts: 36520
Followers: 7066

Kudos [?]: 92912 [0], given: 10528

Re: A jar contains 4 black and 3 white balls.If you pick two [#permalink]

### Show Tags

30 Aug 2013, 05:27
Expert's post
2
This post was
BOOKMARKED
bagdbmba wrote:
A jar contains 4 black and 3 white balls. If you pick two balls at the same time, what's the probability that one ball is black and one is white?

A. 2/7
B. 5/7
C. 4/7
D. 3/7
E. 1/2

P(1st black, 2nd white) = 4/7*3/6 = 4/14;
P(1st white, 2nd black) = 3/7*4/6 = 4/14.

P = 4/14 + 4/14 = 4/7.

OR: $$P=\frac{C^1_4*C^1_3}{C^2_7}=\frac{4}{7}$$

OA is NOT correct.
_________________
BSchool Forum Moderator
Joined: 27 Aug 2012
Posts: 1196
Followers: 129

Kudos [?]: 1457 [0], given: 142

Re: A jar contains 4 black and 3 white balls. If you pick two ba [#permalink]

### Show Tags

30 Aug 2013, 05:48
Thanks Bunuel for pointing it out...Corrected the OA accordingly in the question...
_________________
BSchool Forum Moderator
Joined: 27 Aug 2012
Posts: 1196
Followers: 129

Kudos [?]: 1457 [0], given: 142

Re: A jar contains 4 black and 3 white balls.If you pick two [#permalink]

### Show Tags

05 Sep 2013, 08:26
Bunuel wrote:
bagdbmba wrote:
A jar contains 4 black and 3 white balls. If you pick two balls at the same time, what's the probability that one ball is black and one is white?

A. 2/7
B. 5/7
C. 4/7
D. 3/7
E. 1/2

P(1st black, 2nd white) = 4/7*3/6 = 4/14;
P(1st white, 2nd black) = 3/7*4/6 = 4/14.

P = 4/14 + 4/14 = 4/7.

OR: $$P=\frac{C^1_4*C^1_3}{C^2_7}=\frac{4}{7}$$

OA is NOT correct.

Hi Bunuel,
As per the above explanation - why the OA of the following problem is NOT 3/10?
http://gmatclub.com/forum/x-y-and-z-are-all-unique-numbers-if-x-is-chosen-randomly-159208.html

_________________
Manager
Joined: 23 May 2013
Posts: 127
Followers: 1

Kudos [?]: 55 [0], given: 110

Re: A jar contains 4 black and 3 white balls.If you pick two [#permalink]

### Show Tags

08 Sep 2013, 03:07
Bunuel wrote:
bagdbmba wrote:
A jar contains 4 black and 3 white balls. If you pick two balls at the same time, what's the probability that one ball is black and one is white?

A. 2/7
B. 5/7
C. 4/7
D. 3/7
E. 1/2

P(1st black, 2nd white) = 4/7*3/6 = 4/14;
P(1st white, 2nd black) = 3/7*4/6 = 4/14.

P = 4/14 + 4/14 = 4/7.

OR: $$P=\frac{C^1_4*C^1_3}{C^2_7}=\frac{4}{7}$$

OA is NOT correct.

Hi Bunuel

I wanted to know if probability approach can be used to resolve any sort of probability problem. I am quite comfortable with it. when is it advantageous to use combination approach?
_________________

“Confidence comes not from always being right but from not fearing to be wrong.”

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13414
Followers: 575

Kudos [?]: 163 [0], given: 0

Re: A jar contains 4 black and 3 white balls. If you pick two ba [#permalink]

### Show Tags

16 Mar 2015, 11:55
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: 13414
Followers: 575

Kudos [?]: 163 [0], given: 0

Re: A jar contains 4 black and 3 white balls. If you pick two ba [#permalink]

### Show Tags

06 Jul 2016, 10:39
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 jar contains 4 black and 3 white balls. If you pick two ba   [#permalink] 06 Jul 2016, 10:39
Similar topics Replies Last post
Similar
Topics:
1 In jar A there are 3 white balls and 2 green ones, in jar B there is 2 10 Jul 2016, 07:43
1 There are 3 black balls and 10 white balls. If one is to pick 5 balls, 4 21 Nov 2011, 10:27
43 A bag contains 3 white balls, 3 black balls & 2 red balls 21 29 Aug 2010, 08:06
2 A bag contains 3 white balls, 3 black balls & 2 red balls. 13 10 Aug 2010, 16:41
2 A jar contains only x black balls and y white balls 3 06 Jun 2009, 03:54
Display posts from previous: Sort by
{"found_math": true, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 0, "mathjax_display_tex": 1, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0}