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

It is currently 21 Oct 2014, 22:52

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

From a group of M employees, N will be selected, at random,

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Expert Post
1 KUDOS received
Magoosh GMAT Instructor
User avatar
Joined: 28 Dec 2011
Posts: 2142
Followers: 539

Kudos [?]: 2265 [1] , given: 31

From a group of M employees, N will be selected, at random, [#permalink] New post 07 Aug 2014, 13:58
1
This post received
KUDOS
Expert's post
4
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

42% (01:56) correct 58% (00:56) wrong based on 78 sessions
From a group of M employees, N will be selected, at random, to sit in a line of N chairs. There are absolutely no restrictions, either in the selection process nor in the order of seating — both are entirely random. What is the probability that the employee Andrew is seated somewhere to the right of employee Georgia?
Statement #1: N = 15
Statement #2: N = M



For a set of DS questions on Probability, as well as the OE of this particular question, see:
http://magoosh.com/gmat/2013/gmat-data- ... obability/

Mike :-)
[Reveal] Spoiler: OA

_________________

Mike McGarry
Magoosh Test Prep

Image

Image

Kaplan Promo CodeKnewton GMAT Discount CodesVeritas Prep GMAT Discount Codes
2 KUDOS received
Manager
Manager
User avatar
Joined: 22 Feb 2009
Posts: 229
Followers: 5

Kudos [?]: 45 [2] , given: 138

GMAT ToolKit User CAT Tests
Re: From a group of M employees, N will be selected, at random, [#permalink] New post 07 Aug 2014, 19:36
2
This post received
KUDOS
1
This post was
BOOKMARKED
mikemcgarry wrote:
From a group of M employees, N will be selected, at random, to sit in a line of N chairs. There are absolutely no restrictions, either in the selection process nor in the order of seating — both are entirely random. What is the probability that the employee Andrew is seated somewhere to the right of employee Georgia?
Statement #1: N = 15
Statement #2: N = M



For a set of DS questions on Probability, as well as the OE of this particular question, see:
http://magoosh.com/gmat/2013/gmat-data- ... obability/

Mike :-)


Statement 1: insufficient since we need to know M to solve for the probability
Statement 2: N= M
This turns to sit N people into N chairs
For A is seated somewhere to the right of employee Georgia, we have (1+ 2+ 3+....+ (n-1)) possibilities
To illustrate this, lets say 4 people sit in 4 chairs
G in seat 1, A can be seated in 2,3, and 4 ( 3 possibilities)
G in seat 2, A can be seated in 3,4 ( 2 possibilities)
G in seat 3, A can be seated in 4 only (1 possibility)
Sum = 1+ 2+ 3
After G and A are seated, there are (n-2)! possible combination
( for example, in this case, after G and A are seated, there are two seats left, we have 2! possible combination)
The total possible combinations for N people in N chairs is N!
The possible combinations that meet the requirement is (1+2+3+...(N-1))* (N-2)! = [(N-1)*N/2] * (N-2)!
The probability = [(N-1)*N/2] * (N-2)!/N! = [(N-1)*N/2]/ [(N-1)*N] = 1/2
B is the answer.
_________________

.........................................................................
+1 Kudos please, if you like my post

4 KUDOS received
Tutor
User avatar
Joined: 20 Apr 2012
Posts: 97
Location: Ukraine
GMAT 1: 690 Q51 V31
GMAT 2: 730 Q51 V38
WE: Education (Education)
Followers: 11

Kudos [?]: 120 [4] , given: 30

GMAT ToolKit User
Re: From a group of M employees, N will be selected, at random, [#permalink] New post 08 Aug 2014, 00:01
4
This post received
KUDOS
2
This post was
BOOKMARKED
Mmm:) That's easy.

(1) Not sufficient because we don't know M.
(2) Sufficient.
You need to arrange N people on N seats in such way that the employee Andrew is seated somewhere to the right of employee Georgia. The main idea that you have the same number of possibilities to put Andrew to the right of Georgia and to put him on the left. Just think that in each case when Andrew to the right of Georgia, you can switch their places. That's why, the probability is 1/2.

The correct answer is B.
_________________

I'm happy, if I make math for you slightly clearer
And yes, I like kudos:)

Tutor
User avatar
Joined: 20 Apr 2012
Posts: 97
Location: Ukraine
GMAT 1: 690 Q51 V31
GMAT 2: 730 Q51 V38
WE: Education (Education)
Followers: 11

Kudos [?]: 120 [0], given: 30

GMAT ToolKit User
Re: From a group of M employees, N will be selected, at random, [#permalink] New post 08 Aug 2014, 00:03
You can apply the same idea in this problem if-bob-and-jen-are-two-of-5-participants-in-a-race-how-many-37225.html

Race can finish in 6!=120 ways, and exactly half of them Jen always finishes in front of Bob. The correct answer is 60.
_________________

I'm happy, if I make math for you slightly clearer
And yes, I like kudos:)

Expert Post
Magoosh GMAT Instructor
User avatar
Joined: 28 Dec 2011
Posts: 2142
Followers: 539

Kudos [?]: 2265 [0], given: 31

Re: From a group of M employees, N will be selected, at random, [#permalink] New post 08 Aug 2014, 09:56
Expert's post
Dear smyarga,
Good job! You took the very elegant solution to this. :-)

Dear vad3tha,
You found the answer via brute force calculations, but recognize that this approach can be costly, in terms of time & energy, on the real GMAT. If you want to achieve a truly elite GMAT score, part of what that requires is the ability to see the elegant solutions that involve few or no calculations. See:
http://magoosh.com/gmat/2013/how-to-do- ... th-faster/

Does all this make sense?
Mike :-)
_________________

Mike McGarry
Magoosh Test Prep

Image

Image

Manager
Manager
User avatar
Joined: 22 Feb 2009
Posts: 229
Followers: 5

Kudos [?]: 45 [0], given: 138

GMAT ToolKit User CAT Tests
Re: From a group of M employees, N will be selected, at random, [#permalink] New post 10 Aug 2014, 18:39
mikemcgarry wrote:
Dear smyarga,
Good job! You took the very elegant solution to this. :-)

Dear vad3tha,
You found the answer via brute force calculations, but recognize that this approach can be costly, in terms of time & energy, on the real GMAT. If you want to achieve a truly elite GMAT score, part of what that requires is the ability to see the elegant solutions that involve few or no calculations. See:
http://magoosh.com/gmat/2013/how-to-do- ... th-faster/

Does all this make sense?
Mike :-)


I agree with you, also. This is not what I did when I first saw the problem. I answered by trying out: 4 people in 4 chairs and 5 people in 5 chairs. I came up with 1/2.
I posted this solution afterward in case if ppl want to see the conceptual part the problem. Thanks for reminding me that.
_________________

.........................................................................
+1 Kudos please, if you like my post

Re: From a group of M employees, N will be selected, at random,   [#permalink] 10 Aug 2014, 18:39
    Similar topics Author Replies Last post
Similar
Topics:
2 Experts publish their posts in the topic One number, n, is selected at random from a set of 10 intege rajatr 3 05 May 2013, 21:20
Experts publish their posts in the topic If an employee of Company A is selected at random for a Chembeti 2 29 Feb 2012, 09:11
If a bottle is to be selected at random from a certain Amit05 2 19 Jun 2007, 21:41
1 If an employee of Company A is selected at random for a Riuscita 2 04 Apr 2006, 21:07
If a bottle is to be selected at random from a certain seephani1 2 10 Feb 2006, 14:15
Display posts from previous: Sort by

From a group of M employees, N will be selected, at random,

  Question banks Downloads My Bookmarks Reviews Important topics  


cron

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®.