GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 12 Dec 2018, 04:01

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.

Close

Request Expert Reply

Confirm Cancel
Events & Promotions in December
PrevNext
SuMoTuWeThFrSa
2526272829301
2345678
9101112131415
16171819202122
23242526272829
303112345
Open Detailed Calendar
  • The winning strategy for 700+ on the GMAT

     December 13, 2018

     December 13, 2018

     08:00 AM PST

     09:00 AM PST

    What people who reach the high 700's do differently? We're going to share insights, tips and strategies from data we collected on over 50,000 students who used examPAL.
  • GMATbuster's Weekly GMAT Quant Quiz, Tomorrow, Saturday at 9 AM PST

     December 14, 2018

     December 14, 2018

     09:00 AM PST

     10:00 AM PST

    10 Questions will be posted on the forum and we will post a reply in this Topic with a link to each question. There are prizes for the winners.

If a quality control check is made inspecting a sample of 2

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Senior Manager
Senior Manager
avatar
Joined: 13 Sep 2006
Posts: 255
Location: New York
If a quality control check is made inspecting a sample of 2  [#permalink]

Show Tags

New post Updated on: 13 Dec 2014, 04:48
11
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

88% (00:44) correct 12% (01:08) wrong based on 483 sessions

HideShow timer Statistics

If a quality control check is made inspecting a sample of 2 light bulbs from a box of 12 lighbulbs, how many different samples can be chosen?

A) 6
B) 24
C) 36
D) 66
E) 72

I understand picking 12 options for the 1st light bulb and 11 for the next light bulb but why do you divide this number in half (and how do you know to divide this in half and this will gurantee that all the samples are different?) Thanks

_________________

"Never let the fear of striking out get in your wayâ€


Originally posted by Matrix02 on 05 Nov 2006, 16:59.
Last edited by Bunuel on 13 Dec 2014, 04:48, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.
Manager
Manager
avatar
Joined: 12 Jul 2006
Posts: 112
Re: If a quality control check is made inspecting a sample of 2  [#permalink]

Show Tags

New post 05 Nov 2006, 17:32
3
Try using the formula for combinations:

n!/r!(n-r)!

12!/2!(12-2)!

12!/2!*10!

12*11/2*1

=66
_________________

I think I can. I think I can. I think I can.

Intern
Intern
avatar
B
Joined: 09 Nov 2013
Posts: 11
Re: If a quality control check is made inspecting a sample of 2  [#permalink]

Show Tags

New post 23 May 2016, 20:50
Is there a different way of solving this problem without combinations? Can it be solved with test the answers?
Manager
Manager
avatar
B
Joined: 26 Mar 2017
Posts: 123
Re: If a quality control check is made inspecting a sample of 2  [#permalink]

Show Tags

New post 08 Jun 2017, 10:11
1
rlitagmatstudy wrote:
Is there a different way of solving this problem without combinations? Can it be solved with test the answers?




https://www.khanacademy.org/math/precal ... mbinations

go for it
_________________

I hate long and complicated explanations!

Target Test Prep Representative
User avatar
G
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2830
Re: If a quality control check is made inspecting a sample of 2  [#permalink]

Show Tags

New post 26 Jun 2018, 17:16
Matrix02 wrote:
If a quality control check is made inspecting a sample of 2 light bulbs from a box of 12 lighbulbs, how many different samples can be chosen?

A) 6
B) 24
C) 36
D) 66
E) 72


The number of samples that can be chosen is:

12C2 = 12!/(2! x 10!) = (12 x 11)/2! = 66

Answer: D
_________________

Jeffery Miller
Head of GMAT Instruction

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

GMAT Club Bot
Re: If a quality control check is made inspecting a sample of 2 &nbs [#permalink] 26 Jun 2018, 17:16
Display posts from previous: Sort by

If a quality control check is made inspecting a sample of 2

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


Copyright

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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.