Welcome! Check out our free B-School Guides to learn how you compare with other applicants.

## Probability (Marbles in a bag)

This topic has 1 expert reply and 0 member replies
ashfu2002 Just gettin' started!
Joined
19 Mar 2012
Posted:
4 messages
Probability (Marbles in a bag) Tue Apr 03, 2012 10:22 am
Elapsed Time: 00:00
• Lap #[LAPCOUNT] ([LAPTIME])
A bag contains some red and some blue marbles.How many red marbles are in the bag?

(1) If two marbles are selected from the bag, the probability of selecting one red and one blue marble is 1/4

(2) There are a total of 8 marbles in the bag.

OA E

Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!

### GMAT/MBA Expert

Bill@VeritasPrep GMAT Instructor
Joined
29 Mar 2012
Posted:
1002 messages
Followed by:
138 members
Thanked:
389 times
Target GMAT Score:
800
GMAT Score:
780
Tue Apr 03, 2012 10:48 am
1) There are two ways of getting one blue and one red, each of which has the same probability:

B-R
R-B

Since the total probability is 1/4, P(B-R)=1/8 and P(R-B)=1/8. If we have 7 red and 1 blue, then P(R-B) = 7/8 * 1/7 = 7/56 = 1/8. P(B-R) would have the same probability for a total of 1/4. However, we can also arrive at the same probability if we have 7 blue and 1 red. Insufficient.

2) R + B = 8. There are many possible combinations of red and blue marbles. 1 and 7, 2 and 6, and so on. Insufficient.

When put together, we still have the same possibilities we had in Statement 1, so we still cannot answer.

_________________
Take your GMAT prep on the go!

For the first time, you can complete a full GMAT prep course on your mobile device. Download each of Veritas Prep’s 12 GMAT lessons directly on your iPad and iPhone.

Access The Veritas Prep GMAT Simulator™- for FREE! Veritas Prep has launched their new GMAT Practice Test. Sign up to access the realistic testing environment and challenge yourself today! Get Started Now.

### Best Conversation Starters

1 varun289 40 topics
2 guerrero 21 topics
3 sana.noor 20 topics
4 killerdrummer 19 topics
5 sanaa.rizwan 14 topics
See More Top Beat The GMAT Members...

### Most Active Experts

1 Brent@GMATPrepNow

GMAT Prep Now Teacher

203 posts
2 GMATGuruNY

The Princeton Review Teacher

140 posts
3 Jim@StratusPrep

Stratus Prep

100 posts
4 Anju@Gurome

Gurome

99 posts