• Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

• Get 300+ Practice Questions

Available with Beat the GMAT members only code

• Award-winning private GMAT tutoring
Register now and save up to $200 Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • FREE GMAT Exam Know how you'd score today for$0

Available with Beat the GMAT members only code

## There are three blue marbles, three red marbles ....

tagged by: Vincen

This topic has 2 expert replies and 0 member replies

### Top Member

Vincen Legendary Member
Joined
07 Sep 2017
Posted:
654 messages
Followed by:
3 members
6

#### There are three blue marbles, three red marbles ....

Tue Dec 05, 2017 9:48 am
There are three blue marbles, three red marbles, and three yellow marbles in a bowl. What is the probability of selecting a yellow marble from the bowl on each of three successive draws from the bowl?

A. 2/243
B. 1/27
C. 1/84
D. 2/9
E. 5/21

The OA is C.

What are the formulas I should use here? I can find the correct answer. Experts, may you give me some help please?

### GMAT/MBA Expert

EconomistGMATTutor GMAT Instructor
Joined
04 Oct 2017
Posted:
551 messages
Followed by:
10 members
180
Tue Dec 05, 2017 10:49 am
Hello Vincen.

Let's see what are the formulas here.

We have to pick 1 yellow marble from 3 yellow marbles among 9 total marbles. 3/9=1/3.

Now, we have to pick another yellow marble from 2 yellow marbles among 8 total marbles. 2/8=1/4.

Finally, we have to pick another yellow marble from 1 yellow marble among 7 total marbles. 1/7.

So, the final probability is $$\frac{1}{3}\cdot\frac{1}{4}\cdot\frac{1}{7}=\frac{1}{84}.$$ So, the correct answer is C.

Feel free to ask me again if you have a doubt.

Regards.

_________________
GMAT Prep From The Economist
We offer 70+ point score improvement money back guarantee.
Our average student improves 98 points.

Free 7-Day Test Prep with Economist GMAT Tutor - Receive free access to the top-rated GMAT prep course including a 1-on-1 strategy session, 2 full-length tests, and 5 ask-a-tutor messages. Get started now.

### GMAT/MBA Expert

Matt@VeritasPrep GMAT Instructor
Joined
12 Sep 2012
Posted:
2637 messages
Followed by:
114 members
625
Target GMAT Score:
V51
GMAT Score:
780
Tue Dec 05, 2017 6:36 pm
This isn't really answerable because it isn't clear if we're replacing the marbles between draws. (It *sounds* like we aren't, but it isn't clear.)

If we ARE replacing the marbles, then it's just ((# of yellow marbles) / (# of marbles))Â³

If we AREN'T replacing the marbles, then it's (# of yellow / total) * ((# of yellow - 1)/(total - 1)) * ((# of yellow - 2)/(total - 2)

So the answer's either 1/27 (replacing) or 1/84 (not replacing). Since both answers are there, I'd say you can burn whatever book this came from.

Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now!

### Top First Responders*

1 GMATGuruNY 64 first replies
2 Rich.C@EMPOWERgma... 48 first replies
3 Brent@GMATPrepNow 39 first replies
4 Jay@ManhattanReview 24 first replies
5 Terry@ThePrinceto... 10 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

### Most Active Experts

1 GMATGuruNY

The Princeton Review Teacher

128 posts
2 Rich.C@EMPOWERgma...

EMPOWERgmat

114 posts
3 Scott@TargetTestPrep

Target Test Prep

92 posts
4 Jeff@TargetTestPrep

Target Test Prep

90 posts
5 Max@Math Revolution

Math Revolution

85 posts
See More Top Beat The GMAT Experts