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

It is currently 20 Sep 2018, 19:23

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

A certain ski shop sells pairs of gloves in 12 different colors

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

Hide Tags

Intern
Intern
avatar
B
Joined: 21 Jan 2017
Posts: 33
Re: A certain ski shop sells pairs of gloves in 12 different colors  [#permalink]

Show Tags

New post 10 Jul 2018, 00:56
Bunuel wrote:
aadikamagic wrote:
A certain ski shop sells pairs of gloves in 12 different colors. If one pair of each color is dropped in a bag and a store clerk reaches in to draw two individual gloves simultaneously and at random, what is the probability that she draws two gloves of the same color?

A. 1/144
B. 1/143
C. 1/24
D. 1/23
E. 1/12


We have 2*12 = 24 gloves on the floor. After we pick ANY, there are 23 left and there is only 1 matching pair left for the one we've already picked, so P = 1/23.

Answer: D.

Or: there are 12 matching pairs, and \(C^2_{24}=23*12\) ways to pick any two. P = (favorable)/(total) = 12/(23*12) = 1/23.

Answer: D.

Hope it's clear.



Hi Bunuel,

why is (24c1 * 1) / 24c2 wrong??
As there are 24 gloves, we need to first pick one glove, so 24c1.
Then we have only one way to pick the other glove, so 1.
Total outcomes=picking two out of 24 = 24c2.

we get 2/23, so where am I going wrong? :?

Thanks,
Uma
EMPOWERgmat Instructor
User avatar
V
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 12421
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: Q170 V170
Re: A certain ski shop sells pairs of gloves in 12 different colors  [#permalink]

Show Tags

New post 10 Jul 2018, 19:56
Hi Uma,

There are 12 pairs of gloves - and the prompt asks for the probability of pulling out a pair of matching gloves (NOT a "specific" pair of matching gloves). Thus, the first glove selected can be ANY color (and has an equal probability of being any color) and does not impact the overall calculation. It's the SECOND glove that you have to think about - since it has to match the first glove selected. There will only be 1 glove that matches, out the of the 23 gloves remaining, so the probability will be 1/23. If there wasn't an equal probability of pulling each type of glove on the first try, then the math would be different, but that's not the case here.

GMAT assassins aren't born, they're made,
Rich
_________________

760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save $75 + GMAT Club Tests Free
  Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Intern
Intern
avatar
B
Joined: 21 Jan 2017
Posts: 33
Re: A certain ski shop sells pairs of gloves in 12 different colors  [#permalink]

Show Tags

New post 10 Jul 2018, 23:45
EMPOWERgmatRichC wrote:
Hi Uma,

There are 12 pairs of gloves - and the prompt asks for the probability of pulling out a pair of matching gloves (NOT a "specific" pair of matching gloves). Thus, the first glove selected can be ANY color (and has an equal probability of being any color) and does not impact the overall calculation. It's the SECOND glove that you have to think about - since it has to match the first glove selected. There will only be 1 glove that matches, out the of the 23 gloves remaining, so the probability will be 1/23. If there wasn't an equal probability of pulling each type of glove on the first try, then the math would be different, but that's not the case here.

GMAT assassins aren't born, they're made,
Rich


Ok! Got it. In other words, if they ask you to select a pair from few pairs, we can simply go by this method:
12c1/24c2=1/23.
Re: A certain ski shop sells pairs of gloves in 12 different colors &nbs [#permalink] 10 Jul 2018, 23:45

Go to page   Previous    1   2   [ 24 posts ] 

Display posts from previous: Sort by

A certain ski shop sells pairs of gloves in 12 different colors

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

Events & Promotions

PREV
NEXT


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®.