It is currently 29 Jun 2017, 07:59

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# In a room filled with 7 people, 4 people have exactly 1

 post reply Question banks Downloads My Bookmarks Reviews Important topics
Author Message
Manager
Joined: 29 Jul 2007
Posts: 182
In a room filled with 7 people, 4 people have exactly 1 [#permalink]

### Show Tags

18 Nov 2007, 12:48
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

In a room filled with 7 people, 4 people have exactly 1 friend in the room and 3 people have exactly 2 friends in the room (Assuming that friendship is a mutual relationship, i.e. if John is Peter's friend, Peter is John's friend). If two individuals are selected from the room at random, what is the probability that those two individuals are NOT friends?

a)5/21
b)3/7
c)4/7
d)5/7
e)16/21
CEO
Joined: 17 Nov 2007
Posts: 3584
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40

### Show Tags

18 Nov 2007, 13:18
e

p=1-q=1-(4*1/6+3*2/6)/7=1-5/21=16/21
Manager
Joined: 26 Sep 2007
Posts: 65

### Show Tags

18 Nov 2007, 18:54
walker wrote:
e

p=1-q=1-(4*1/6+3*2/6)/7=1-5/21=16/21

Walker, could you please explain in more detail?
VP
Joined: 08 Jun 2005
Posts: 1145

### Show Tags

18 Nov 2007, 19:18
4/7)*(1/6) = 4/42 (choosing a person that has only 1 friend out of seven and choosing his friend out of 6)

(3/7)*(2/6) = 6/42 (choosing a person that has 2 friends out of seven and choosing his friend , he has two, out of 6)

4/42+6/42 = 10/42 = 5/21

but we need 1-(5/21) = 16/21

the answer is (E)

Manager
Joined: 26 Sep 2007
Posts: 65

### Show Tags

18 Nov 2007, 19:47
KillerSquirrel wrote:
4/7)*(1/6) = 4/42 (choosing a person that has only 1 friend out of seven and choosing his friend out of 6)

(3/7)*(2/6) = 6/42 (choosing a person that has 2 friends out of seven and choosing his friend , he has two, out of 6)

4/42+6/42 = 10/42 = 5/21

but we need 1-(5/21) = 16/21

the answer is (E)

KillerSquirrel, thanks for the explanation.
Manager
Joined: 03 Sep 2006
Posts: 233

### Show Tags

18 Nov 2007, 20:23
KillerSquirrel, thanks a lot - I was lost in this Q ...
18 Nov 2007, 20:23
Display posts from previous: Sort by

# In a room filled with 7 people, 4 people have exactly 1

 post reply Question banks Downloads My Bookmarks Reviews Important topics

 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®.