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Math Help - Sample tossing coin question

  1. #1
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    Sample tossing coin question

    Dear all, don't know what went wrong with my solution, it doesn't make sense!

    Question: Toss a coin twice. What is the probability of getting first toss a head OR second toss a tail?

    My solution:
    HH, HT, TH, TT
    2/4 + 2/4 = 1 ??? Doesn't make sense, why?

    Thanks!!!
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  2. #2
    Jen
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    Quote Originally Posted by mak15 View Post
    Dear all, don't know what went wrong with my solution, it doesn't make sense!

    Question: Toss a coin twice. What is the probability of getting first toss a head OR second toss a tail?

    My solution:
    HH, HT, TH, TT
    2/4 + 2/4 = 1 ??? Doesn't make sense, why?

    Thanks!!!
    The Probability of P(A \cup B) = P(A)+P(B)-P(A \cap B)

    The probability of the first event is 2/4 the probability of the second event is 2/4 and the probability of both it 1/4 so,

    \frac{2}{4}+\frac{2}{4}-\frac{1}{4}=\frac{3}{4}

    Which, if you look at the possibilities that you wrote out, this solution makes sense.

    Hope that helps.
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