Find all School-related info fast with the new School-Specific MBA Forum

It is currently 25 Oct 2014, 14:36

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

In a box of 12 pens, a total of 3 are defective. If a

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
avatar
Joined: 08 Nov 2008
Posts: 38
Followers: 0

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

In a box of 12 pens, a total of 3 are defective. If a [#permalink] New post 08 Nov 2008, 18:45
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

33% (01:01) correct 67% (01:19) wrong based on 7 sessions
In a box of 12 pens, a total of 3 are defective. If a customer buys 2 pens selected at random from the box, what is the probability that neither pen will be defective?

A. 1/6
B. 2/9
C. 6/11
D. 9/16
E. 3/4
Intern
Intern
User avatar
Joined: 14 Sep 2003
Posts: 46
Location: california
Followers: 1

Kudos [?]: 14 [0], given: 0

Re: pens--29 [#permalink] New post 08 Nov 2008, 18:59
# defective pens = 3
# good pens = 9

Probability of the 1st pen being good = # of favorable outcomes / # of total outcomes = 9/12

Probability of the 2nd pen being good = # of remaining favorable outcomes / # of total remaining outcomes = 8 / 11

Total probability = 9/12 * 8/11 = 6/11

My pick C
_________________

excellence is the gradual result of always striving to do better

Manager
Manager
User avatar
Joined: 05 Jul 2008
Posts: 139
GMAT 1: Q V
GMAT 2: 740 Q51 V38
Followers: 2

Kudos [?]: 68 [0], given: 40

Re: pens--29 [#permalink] New post 08 Nov 2008, 19:51
gorden wrote:
In a box of 12 pens, a total of 3 are defective. If a customer buys 2 pens selected at random from the box, what is the probability that neither pen will be defective?

A. 1/6
B. 2/9
C. 6/11
D. 9/16
E. 3/4


I have another way to solve by using combinations.
First, there are 9C2 ways you can select 2 good pencils from 9 good ones.
Second, there are 12C2 ways you select 2 pencils from 12 ones in the box.
Then, the probability that neither pen will be defective is: 9C2/12C2=6/11

Song of the day: To be with you- David Archuleta
Intern
Intern
avatar
Joined: 21 Oct 2010
Posts: 3
Followers: 0

Kudos [?]: 0 [0], given: 1

Re: pens--29 [#permalink] New post 09 Jul 2011, 20:36
Thanks all for the answer. I'm doing this question and do not know why I was wrong.
This is the way how I solve this: calculating the probability both of pens he pick are defective then take 1 subtract the result.
1st is defective = 3/12
2nd is defective = 2/11
--> pro. of chance both is defective is: 3/12 * 2/11 = 21/22
--> pro. of chane neither is defective is: 1 - 21/22 = 1/22

(Yep, There is no result like this in the choice. I just want to know why I was wrong.)
Thanks much!
Expert Post
1 KUDOS received
Veritas Prep GMAT Instructor
User avatar
Joined: 16 Oct 2010
Posts: 4877
Location: Pune, India
Followers: 1157

Kudos [?]: 5382 [1] , given: 165

Re: pens--29 [#permalink] New post 13 Jul 2011, 04:04
1
This post received
KUDOS
Expert's post
dizim wrote:
Thanks all for the answer. I'm doing this question and do not know why I was wrong.
This is the way how I solve this: calculating the probability both of pens he pick are defective then take 1 subtract the result.
1st is defective = 3/12
2nd is defective = 2/11
--> pro. of chance both is defective is: 3/12 * 2/11 = 21/22
--> pro. of chane neither is defective is: 1 - 21/22 = 1/22

(Yep, There is no result like this in the choice. I just want to know why I was wrong.)
Thanks much!


You are not getting the right answer because there is another case: Probability that only one pen is defective.
Probability that both are defective + Probability that only one is defective + Probability that neither is defective = 1
You need to calculate the probability that only is defective as well and subtract that from 1 too.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Save $100 on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.

Veritas Prep Reviews

Intern
Intern
avatar
Joined: 21 Oct 2010
Posts: 3
Followers: 0

Kudos [?]: 0 [0], given: 1

Re: pens--29 [#permalink] New post 13 Jul 2011, 05:51
Thanks VeritasPrepKarishma!
Kudos for you ^^
Re: pens--29   [#permalink] 13 Jul 2011, 05:51
    Similar topics Author Replies Last post
Similar
Topics:
6 Experts publish their posts in the topic A company that ships boxes to a total of 12 distribution chintzzz 8 16 Jun 2010, 08:23
A company that ships boxes to a total of 12 distribution hbs2012 3 16 Oct 2008, 12:45
In a box of 12 pens, a total of 3 are defective. If a puma 1 23 May 2008, 11:03
A company that ships boxes to a total of 12 distribution alimad 2 01 Oct 2007, 03:01
A company that ships boxes to a total of 12 distribution rahulraao 7 09 Sep 2005, 19:44
Display posts from previous: Sort by

In a box of 12 pens, a total of 3 are defective. If a

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.