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By using binomial distribution if two coin are tossed 4 times ,find?

  1. May 7, 2010 #1
    by using binomial distribution if two coin are tossed 4 times ,find?
    1)the probability of 2 heads in 4 times ?
    2)the probability of less than one head once?
    3)the probability of than 2 tails in 3 times ?
    4)the expected number of two tails ?
    5)the variance of the number of 2 heads?
     
    Last edited by a moderator: May 8, 2010
  2. jcsd
  3. May 7, 2010 #2

    tiny-tim

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    Welcome to PF!

    Hi mattamimi! Welcome to PF! :wink:

    Show us what you've tried, and where you're stuck, and then we'll know how to help …

    start with 1). :smile:
     
  4. May 7, 2010 #3
    thank you :)


    1.) I think P(x)=4C1*(1/4)^1*(3/4)^3=0.421
     
  5. May 7, 2010 #4

    tiny-tim

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    (try using the X2 tag just above the Reply box :wink:)

    uhh? that's obviously the probability of one head in 4 times
     
  6. May 7, 2010 #5
    sorry,but I couldn't solve it,can you solve the first problem
     
  7. May 7, 2010 #6

    tiny-tim

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    Sorry, but you have to do it yourself.

    Please can I check that I understand 1) correctly …

    is 1) asking for the probability that when 2 coins are tossed 4 times, there will be 2 heads 4 times, ie a total of 8 heads, ie all heads?

    And is 2) asking for the probability that there will be 2 tails exactly once (so the other three times are either 2 heads or one of each)?

    And what is the missing word in 3)?
     
  8. May 7, 2010 #7

    Redbelly98

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    Moderator's note: thread moved from "Set Theory, Logic, Probability, Statistics"
     
  9. May 8, 2010 #8
    I think I speak for tiny-tim as well as for myself:
    "YES".

    Just to clarify, you are flipping two coins and recording the number of heads. Then you repeat this until you have FOUR numbers?
     
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