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

 It is currently 05 May 2015, 03:01

### 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 how many ways can 6 ppl be seated in a circle if 2 ppl

Author Message
TAGS:
CEO
Joined: 15 Aug 2003
Posts: 3469
Followers: 61

Kudos [?]: 702 [0], given: 781

In how many ways can 6 ppl be seated in a circle if 2 ppl [#permalink]  01 Oct 2003, 13:22
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
In how many ways can 6 ppl be seated in a circle if 2 ppl are always separated.

Two girls have their birthdays in the same week.It is known that one
of the girls was born on a saturday. determine the prob that both
were born on a saturday.
Intern
Joined: 29 Aug 2003
Posts: 49
Location: Detroit, MI
Followers: 0

Kudos [?]: 2 [0], given: 0

Re: PS : Counting Methods and Probability [#permalink]  02 Oct 2003, 06:06
praetorian123 wrote:
In how many ways can 6 ppl be seated in a circle if 2 ppl are always separated.

Two girls have their birthdays in the same week.It is known that one
of the girls was born on a saturday. determine the prob that both
were born on a saturday.

Let me try ....

The total number of ways in which N people can be seated in a circle = (N - 1)!

If two people (say A and B) are next to each other, the remaining (N-2) people can be arranged in (N-2)! ways - in one direction and (N-2)! more ways in the other direction i.e. 2*(N-2)! ways

So, answer = (N - 1)! - 2*(N-2)! = 5! - 2*4! = 120 - 48 = 72

I think this can be generalized to say that of N people, 2*(N-t)! ways exist in which t of N are next to one another, where t < N and (N-1)! - 2*(N-t)! ways exist in which t of N people are not next to one another.

Am I right?

Is the answer 1/7 for the second one?

Given that the two girls were born in the same week, the probability will be 1 of the seven days.
Re: PS : Counting Methods and Probability   [#permalink] 02 Oct 2003, 06:06
Similar topics Replies Last post
Similar
Topics:
How imp is the data plan and how many ppl have data plan ... 4 27 Sep 2009, 07:17
In how many ways can 6 people be arranged in a circle if 2 6 14 Jun 2007, 20:05
8 In how many ways can 6 people be seated at a round table if 10 15 Oct 2006, 08:32
In how many ways 5 boys and 6 girls can be seated on 12 5 22 Jan 2006, 00:44
How many different ways can 2 students be seated in a row of 5 12 Nov 2005, 23:29
Display posts from previous: Sort by