It is currently 23 Jun 2017, 10:55

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

Probability

Author Message
Senior Manager
Joined: 11 Nov 2003
Posts: 356
Location: Illinois

Show Tags

11 Feb 2004, 13:57
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

There are 4 identical balls (same size). Each ball could be either RED or WHITE only. What is the probability that there are 2 RED and 2 WHITE balls?
Director
Joined: 03 Jul 2003
Posts: 652

Show Tags

11 Feb 2004, 14:17
P(2W&2R) = 3/8
SVP
Joined: 30 Oct 2003
Posts: 1790
Location: NewJersey USA

Show Tags

11 Feb 2004, 14:34
I get 1/4 as the answer.

Each ball can either be RED or WHITE so we have 4 balls hence 2^4 = 16 combinations. Out of these 2W and 2R occur 4 times as follows

WWRR
RRWW
WRWR
RWRW
Hence 4/16 = 1/4
Senior Manager
Joined: 11 Nov 2003
Posts: 356
Location: Illinois

Show Tags

11 Feb 2004, 14:36
anandnk wrote:
I get 1/4 as the answer.

Each ball can either be RED or WHITE so we have 4 balls hence 2^4 = 16 combinations. Out of these 2W and 2R occur 4 times as follows

WWRR
RRWW
WRWR
RWRW
Hence 4/16 = 1/4

Anand,

You missed WRRW and RWWR
SVP
Joined: 30 Oct 2003
Posts: 1790
Location: NewJersey USA

Show Tags

11 Feb 2004, 14:37
Oops my bad. You are right
No of ways you can arrange 2 W and 2R = 4!/(2!*2!) = 6
Total combinations = 16
so P = 6/16 = 3/8
Manager
Joined: 28 Jan 2004
Posts: 203
Location: India

Show Tags

12 Feb 2004, 06:14
It is not arrangement ...so there is no difference between WRRW and RWWR!!!!!!!!!!!!!!
Please let me know if my approach is incorrect.

RED BLUE
4 0
3 1
2 2
1 3
0 4

So the probability is 1/5..............
Probability is my weakest...so please pardon me if i did a stupid analysis...and if anyone is posting a reply to my reply the please just copy and send that to me as PM also because tomorrow i will not be able to track this question!!!!! i don't know how to do that if it can be done..and i am sure that is some way of doing that....................
GMAT Instructor
Joined: 07 Jul 2003
Posts: 770
Location: New York NY 10024
Schools: Haas, MFE; Anderson, MBA; USC, MSEE

Show Tags

12 Feb 2004, 11:31
mdfrahim wrote:
It is not arrangement ...so there is no difference between WRRW and RWWR!!!!!!!!!!!!!!
Please let me know if my approach is incorrect.

RED BLUE
4 0
3 1
2 2
1 3
0 4

So the probability is 1/5..............
Probability is my weakest...so please pardon me if i did a stupid analysis...and if anyone is posting a reply to my reply the please just copy and send that to me as PM also because tomorrow i will not be able to track this question!!!!! i don't know how to do that if it can be done..and i am sure that is some way of doing that....................

You counted the "outcomes" but they're are not equally likely, hence, you cannot figure out the probability that way.
_________________

Best,

AkamaiBrah
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993

Manager
Joined: 28 Jan 2004
Posts: 203
Location: India

Show Tags

13 Feb 2004, 02:10
Well ,Probability = favourable events/total number of events
Sorry to say , i am not yet satisfied......is somebody there to elaborate on this.

Thanks.
13 Feb 2004, 02:10
Display posts from previous: Sort by