Results 1 to 7 of 7

Math Help - Conditional probability problem

  1. #1
    Newbie
    Joined
    Jan 2011
    Posts
    15

    Conditional probability problem

    A box contains 4 fair coins, and one two headed coin. A man selects a coin from the box, tosses it twice, and gets two heads. What is the probability that he selected the two headed coin?

    Possible answers: 1/5, 1/3, 1/2, 4/5, 2/3.

    My answer was 1/2. Can anyone disprove this?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Behold, the power of SARDINES!
    TheEmptySet's Avatar
    Joined
    Feb 2008
    From
    Yuma, AZ, USA
    Posts
    3,764
    Thanks
    78
    Quote Originally Posted by smallfry View Post
    A box contains 4 fair coins, and one two headed coin. A man selects a coin from the box, tosses it twice, and gets two heads. What is the probability that he selected the two headed coin?

    Possible answers: 1/5, 1/3, 1/2, 4/5, 2/3.

    My answer was 1/2. Can anyone disprove this?
    I assume that you know Bayes' theorem

    Let A be the event that you draw the two headed coin and
    Let B be the event that you get two heads then

    \displaystyle P(A|B)=\frac{P(B|A)P(A)}{P(B)}=...
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jan 2011
    Posts
    15
    Yes, I know Bayes' theorem. So the answer IS 1/2 right?
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Behold, the power of SARDINES!
    TheEmptySet's Avatar
    Joined
    Feb 2008
    From
    Yuma, AZ, USA
    Posts
    3,764
    Thanks
    78
    did you plug in the numbers? Please show your work!
    Follow Math Help Forum on Facebook and Google+

  5. #5
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    I got 1/2
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Newbie
    Joined
    Jan 2011
    Posts
    15
    Ok I did it, and the answer is 1/2. Thanks guys I figured it out with a probability tree.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    MHF Contributor matheagle's Avatar
    Joined
    Feb 2009
    Posts
    2,763
    Thanks
    5
    It's

    {1/5\over (1)(1/5)+(1/4)(4/5)}
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Conditional Probability Problem
    Posted in the Statistics Forum
    Replies: 3
    Last Post: February 16th 2011, 05:43 PM
  2. Help! Conditional Probability-Urn Problem
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: December 13th 2009, 09:38 PM
  3. conditional probability problem
    Posted in the Statistics Forum
    Replies: 1
    Last Post: July 13th 2009, 10:44 PM
  4. Urn problem - conditional probability
    Posted in the Advanced Statistics Forum
    Replies: 2
    Last Post: September 10th 2008, 10:45 PM
  5. Conditional probability problem
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: January 27th 2008, 01:10 PM

Search Tags


/mathhelpforum @mathhelpforum