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Simple probability

  1. Jul 8, 2010 #1
    A fair coin is tossed five times. What is the probability of obtaining three heads and two tails?

    I cannot find out the right answer by my way

    Ans: 5/16

    Thanks :)
  2. jcsd
  3. Jul 8, 2010 #2


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    Homework Helper

    Since there are only two possibilities for each flip (head or tail), if you find the probability of having exactly 3 heads you've got the question answered. what distribution do you know of that

    - deals with counts of a particular outcome
    - assumes only two possible outcomes per trial
    - assumes that successive trials are independent
  4. Jul 8, 2010 #3
    Yes the Bernoulli Trial formula will directly yield the answer for n=5, p=0.5 and k=3.

    Another way is this.
    Total possible outcomes is 2^5=32
    How can you Permute [arrange] 5 items, 5 at a time, with 3 the same and 2 the same ?
    5 ! / [ (5-5)! 3! 2! = 10
    10/32 = 5/16
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