It is currently 23 Nov 2020, 22:53
My Tests

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

A bag contains 3 white, 4 black, and 2 red marbles. Two marb

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Founder
Founder
User avatar
Joined: 18 Apr 2015
Posts: 13883
GRE 1: Q160 V160
Followers: 313

Kudos [?]: 3673 [0], given: 12901

CAT Tests
A bag contains 3 white, 4 black, and 2 red marbles. Two marb [#permalink] New post 15 Sep 2017, 07:47
Expert's post
00:00

Question Stats:

59% (01:34) correct 40% (01:40) wrong based on 42 sessions
1 KUDOS received
Director
Director
Joined: 03 Sep 2017
Posts: 518
Followers: 2

Kudos [?]: 440 [1] , given: 66

Re: A bag contains 3 white, 4 black, and 2 red marbles. Two marb [#permalink] New post 21 Sep 2017, 05:13
1
This post received
KUDOS
The probability of extracting a red marble in the second draw is equal to the probability of extracting whatever marble in the first draw times the probability of extracting a red marble in the second draw, i.e. 1*2/9 = 2/9. Answer D!
1 KUDOS received
Intern
Intern
Joined: 08 Dec 2017
Posts: 40
Followers: 1

Kudos [?]: 46 [1] , given: 70

Re: A bag contains 3 white, 4 black, and 2 red marbles. Two marb [#permalink] New post 04 Mar 2018, 05:40
1
This post received
KUDOS
The scenario of getting a red marble in the second draw could be like this:
1) no red in first draw and a red in the second draw
2) a red in the first draw and a red in the second draw

1) (7/9)*(2/8)=7/36
2) (2/9)*(1/8)=1/36

So, the probability that the second marble is drawn will be red = (7/36)+(1/36)=2/9

The answer is D.
Target Test Prep Representative
User avatar
Status: Head GRE Instructor
Affiliations: Target Test Prep
Joined: 09 May 2016
Posts: 161
Location: United States
Followers: 8

Kudos [?]: 201 [0], given: 0

Re: A bag contains 3 white, 4 black, and 2 red marbles. Two marb [#permalink] New post 13 May 2018, 16:45
Expert's post
Carcass wrote:



A bag contains 3 white, 4 black, and 2 red marbles. Two marbles are drawn from the bag. If replacement is not allowed, what is the probability that the second marble drawn will be red?

A. \(\frac{1}{36}\)

B. \(\frac{1}{12}\)

C. \(\frac{7}{36}\)

D. \(\frac{2}{9}\)

E. \(\frac{7}{9}\)


If a red marble is selected first and a red marble is selected second, the probability is:

2/9 x 1/8 = 2/72

If a red marble is not selected first and a red marble is selected second, the probability is:

7/9 x 2/8 = 14/72

So the overall probability is 2/72 + 14/72 = 16/72 = 2/9.

Answer: D
_________________

Jeffrey Miller

Head of GRE Instruction

Jeff@TargetTestPrep.com
TTP - Target Test Prep Logo
41 Reviews

5-star rated online GRE quant
self study course

See why Target Test Prep is the top rated GRE quant course on GRE Prep Club. Read Our Reviews

1 KUDOS received
GRE Instructor
User avatar
Joined: 10 Apr 2015
Posts: 3905
Followers: 163

Kudos [?]: 4761 [1] , given: 70

Re: A bag contains 3 white, 4 black, and 2 red marbles. Two marb [#permalink] New post 19 Nov 2020, 10:57
1
This post received
KUDOS
Expert's post
Carcass wrote:



A bag contains 3 white, 4 black, and 2 red marbles. Two marbles are drawn from the bag. If replacement is not allowed, what is the probability that the second marble drawn will be red?

A. \(\frac{1}{36}\)

B. \(\frac{1}{12}\)

C. \(\frac{7}{36}\)

D. \(\frac{2}{9}\)

E. \(\frac{7}{9}\)


This question reminds me of my childhood, when my friends and I would sometimes "draw straws" to randomly select one person to do something awful.
Someone would hold up n pieces of grass (for n people), and one of those pieces was very short. The person who selected the shortest piece was the one who had to perform the task.

There was always one guy who wanted to choose his piece last. His reasoning was that his chances of drawing the shortest piece would be minimized, since every person before him had a chance of drawing the short piece before it got to his turn.

The truth of the matter is that each of the n people had a 1/n chance of selecting the shortest piece, regardless of the order in which they selected a straw.

The same applies to the original question here.

2 of the 9 marbles are red, so P(red ball selected SECOND) = P(red ball selected FIRST) = 2/9

Cheers,
Brent
_________________

Brent Hanneson – Creator of greenlighttestprep.com
Image
Sign up for GRE Question of the Day emails

Re: A bag contains 3 white, 4 black, and 2 red marbles. Two marb   [#permalink] 19 Nov 2020, 10:57
Display posts from previous: Sort by

A bag contains 3 white, 4 black, and 2 red marbles. Two marb

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

GRE Prep Club Forum Home| About| Terms and Conditions and Privacy Policy| GRE Prep Club Rules| Contact

Powered by phpBB © phpBB Group

Kindly note that the GRE® test is a registered trademark of the Educational Testing Service®, and this site has neither been reviewed nor endorsed by ETS®.