Results 1 to 2 of 2

Math Help - A question on: Taking 2 fail products of 20

  1. #1
    Junior Member
    Joined
    Jul 2008
    From
    Athens, Greece
    Posts
    48

    20 items, 8 are failed, probability to coose 2 failed items..

    Hello,

    Sorry for not being clear I am editing my question, I myself had not read it thoroughly, (was tired at the time)...

    This is the exercise:

    There are 20 items in total. Among them there are 8 failed items. We choose randomly 2 items. What is the proability that these 2 items are both failed.


    Soltion (in the book):

    Threre are C(20,2) ways we can choose 2 any items.There are C(18,2) ways we can take 2 failed items. And the probability is C(18,2)/C(20,2).



    I am sure this is trivial exercise containing a typographical error, and we should have C(8,2) insted of C(18,2), right?

    Thank you very much!

    My aplogies again for not being clear!
    Last edited by Melsi; October 7th 2011 at 05:38 AM. Reason: Making the question clear
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5

    Re: A question on: Taking 2 fail products of 20

    Quote Originally Posted by Melsi View Post
    Hello,

    We choose 2 products of 20, this is C(20,2) different ways (this is clear).

    Then for both products being failed there are C(18,2) ways we can choose. This one I don't get it!?

    Solution= C(18,2)/C(20,2) Why??

    In addition I can understand very well this problem, choosing two asses from 52 cards = C(4,2)/C(52,2).

    Can the last problem help me somehow understand the first one, do they relate in any way?

    Thank you very much!
    Post the whole question. We are not mind readers, although if I had to attempt it I'd guess that the question is something like: 18 of 20 products are faulty. You choose 2. Find the probability that both are faulty.

    But the fact is that we shouldn't have to be mind readers. If you want help, you're meant to make it easy for people to help ....
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Question about inner products
    Posted in the Advanced Algebra Forum
    Replies: 1
    Last Post: November 11th 2009, 05:00 AM
  2. Replies: 1
    Last Post: October 29th 2009, 01:32 PM
  3. Question about taking a derivative
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 30th 2009, 01:21 PM
  4. Replies: 1
    Last Post: October 31st 2008, 11:21 PM
  5. Special Products Question
    Posted in the Algebra Forum
    Replies: 1
    Last Post: March 20th 2008, 05:00 AM

Search Tags


/mathhelpforum @mathhelpforum