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Easy Question-Guo

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  • Easy Question-Guo

    p40 in Guo Manual Problem 6

    "You first toss a coin. If you get heads, then you throw a die; if you get tails, then you toss another coin"

    (3) The probability that you get heads and the number 6

    I thought the answer would be 1/12, because 1/2 the time you get heads, so (heads,roll1)+(heads,roll2)+(heads,roll2)+(heads,r oll2)+(heads,roll2)+(heads,roll2)=1/2, so each one being equally likely, they would each have a probability of 1/12.
    But the manual says the probability is 1/8.
    Is this correct?
    If so, how does it relate to all the heads outcomes adding up to 1/2?

  • #2
    It looks as it is assumed the you can throw a die as well after tossing a coin the second time.

    The probability to have a head after two attempts is 3/4: p+q*p, where q = 1-p, and p=1/2. Or, if you want, 1-q^2.

    Multiplying 3/4 by 1/6 we get 1/8.
    Last edited by yurakm; November 25 2005, 12:15 PM.


    • #3
      yeah I ended up writing the author, and he said it was just a mistake, but that's probably what was originally meant. Thanks for taking the time to look, I should have thought of that too.