Sponsored Ad:
See the top rated post in this thread. Click here

Results 1 to 5 of 5

Thread: Help me with this probablity problem

  1. #1
    Trying to make mom and pop proud
    Join Date
    May 2014
    Posts
    1
    Rep Power
    7


    Good post? Yes | No

    Help me with this probablity problem

    Sponsored Ad:
    If 12 persons are seated at a round table, what is the probability that two particulars persons
    sit together?

  2. #2
    Trying to make mom and pop proud
    Join Date
    Jul 2014
    Posts
    1
    Rep Power
    6


    Good post? Yes | No

    Answer

    12 persons can sit along around a table in (12-1)! ways i.e 11!
    Now considering that the 2 members who has to sit together as one unit, we have 11 units altogether, who can sit along in (11-1)! i.e 10! ways

    Also the 2 persons sitting together can exchange their positions in 2! ways

    So the probability is (10! * 2)/11! = 2/11

  3. #3
    GRE-GMAT Instructor Brent Hanneson's Avatar
    Join Date
    Apr 2011
    Location
    Vancouver, Canada
    Posts
    362
    Rep Power
    11


    1 out of 1 members found this post helpful. Good post? Yes | No
    Quote Originally Posted by Rakibul Raju View Post
    If ‘12’ persons are seated at a round table, what is the probability that two particulars persons
    sit together?
    We don't need to apply any counting techniques if we look at it this way: What is the probability that Ann and Bea sit together.
    Let's just focus on Ann for a moment.
    What is the probability that Bea is sitting beside her?
    Well, there are 11 remaining seats and 2 of them are beside Ann.
    So, P( Ann and Bea sit together) = 2/11

    Cheers,
    Brent

  4. #4
    Trying to make mom and pop proud
    Join Date
    Dec 2015
    Posts
    2
    Rep Power
    5


    Good post? Yes | No

    Re: Help me with this probablity problem

    Quote Originally Posted by Brent Hanneson View Post
    We don't need to apply any counting techniques if we look at it this way: What is the probability that Ann and Bea sit together.
    Let's just focus on Ann for a moment.
    What is the probability that Bea is sitting beside her?
    Well, there are 11 remaining seats and 2 of them are beside Ann.
    So, P( Ann and Bea sit together) = 2/11

    Cheers,
    Brent
    Why is it that the number of ways 12 people can be seated at a round table is 11!? Why not 12!? explain please? and also the rest of the proces please.

    Thanks

  5. #5
    GRE-GMAT Instructor Brent Hanneson's Avatar
    Join Date
    Apr 2011
    Location
    Vancouver, Canada
    Posts
    362
    Rep Power
    11


    Good post? Yes | No

    Re: Help me with this probablity problem

    Quote Originally Posted by optimus141 View Post
    Why is it that the number of ways 12 people can be seated at a round table is 11!? Why not 12!? explain please? and also the rest of the proces please.

    Thanks
    You will notice that I never said that 12 people can be seated at a round table in 11! ways (Chromepal made this claim). I'm not a big fan of "people sitting at a circle" questions, because the assumption is that the seats are identical. Since this is not stated in the question, I solved it in a way that does not require us to make this assumption.

    Cheers,
    Brent

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Probablity problem
    By babaikaushik in forum GMAT Problem Solving
    Replies: 1
    Last Post: 03-22-2009, 05:07 AM
  2. Probablity problem - Please advice
    By babaikaushik in forum GMAT Problem Solving
    Replies: 1
    Last Post: 03-21-2009, 06:14 PM
  3. Probablity
    By tycoonpt in forum GMAT Problem Solving
    Replies: 9
    Last Post: 02-17-2009, 06:30 PM
  4. Probablity - Problem Solving
    By Tom_Harpic in forum GMAT Math
    Replies: 0
    Last Post: 01-06-2007, 12:25 AM
  5. A simple probablity problem
    By stickler_nishat in forum GRE Math
    Replies: 14
    Last Post: 10-29-2005, 10:56 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •