Results 1 to 3 of 3

Math Help - Probabilities of correct answers

  1. #1
    Newbie
    Joined
    Jul 2012
    From
    CA
    Posts
    8

    Probabilities of correct answers

    You are lost in the National Park. Tourists (which look just like indians) comprise two-thirds of the visitors to the park, and give a correct answer to requests for directions with probability 3/4. (Answers to repeated questions are independent, even if the question and the person are the same.) If you ask an indian for directions, the answer is always incorrect.

    (a) You ask a passerby whether the exit from the Park is East or West. The answer is East.

    What is the probability that this is correct?
    (2/3)(3/4) + (1/3)(0) = 1/2


    (b) You ask the same person again, and receive the same reply. What is the probability of being

    correct?

    1/2^2 ?

    (c) You ask the same person for the third time, and receive the same reply. What is the probability

    of being correct?
    1/2^3 ?


    (d) You ask for the fourth time, and receive the same reply. What is the probability of being
    correct?
    1/2^4?


    (e) Had the fourth answer been West instead, what is the probability of East being correct?
    1/2^4 ?


    (f) Contrast your answers in part d and part e and explain.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    May 2010
    Posts
    1,030
    Thanks
    28

    Re: Probabilities of correct answers

    (a) fine

    (b) p(2 correct answers|indian)*p(indian) + p(2 correct answers|tourist)*p(tourist)
    0*1/3 + 0.75^2 = 9/16

    (c)
    use the same method as (b)

    (d)
    use the same method as (c)

    (e)
    This person has given different replies, so must be a tourist. what is the probability of a tourist giving 3 correct answers out of 4?

    (f)
    should follow from (d) and (e).
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jul 2012
    From
    CA
    Posts
    8

    Re: Probabilities of correct answers

    Quote Originally Posted by SpringFan25 View Post
    (a) fine

    (b) p(2 correct answers|indian)*p(indian) + p(2 correct answers|tourist)*p(tourist)
    0*1/3 + 0.75^2 = 9/16
    What happened to the 2/3?
    p(2 correct answers|indian)*p(indian) + p(2 correct answers|tourist)*p(tourist)
    0*1/3 + (2/3) 0.75^2 ??

    This person has given different replies, so must be a tourist. what is the probability of a tourist giving 3 correct answers out of 4?
    (2/3)(3/4)^3(1/4) ??
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Are my answers correct ?
    Posted in the Number Theory Forum
    Replies: 2
    Last Post: October 9th 2012, 08:55 AM
  2. Are my answers correct? thank you.
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: December 4th 2009, 02:03 PM
  3. Are my answers correct
    Posted in the Geometry Forum
    Replies: 1
    Last Post: September 26th 2009, 06:58 PM
  4. Are my answers correct?
    Posted in the Pre-Calculus Forum
    Replies: 9
    Last Post: August 30th 2009, 03:01 PM
  5. Are my answers correct?
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: August 27th 2009, 03:46 PM

Search Tags


/mathhelpforum @mathhelpforum