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Math Help - [SOLVED] coin probability problem

  1. #1
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    [SOLVED] coin probability problem

    Kaplan Page 136 #19

    If 3 coins are tossed simultaneously, what is the probability of getting exactly 2 tails?

    The answer is 3/8. Instead of listing all the cases, is there a faster way to solve this problem?

    Thanks in advance
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  2. #2
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    Every coin flip has a \frac{1}{2} chance of turning up heads or tails.

    You can have T, T, H or T, H, T or H, T, T
    Each of these 3 outcomes has a probability of \frac{1}{2} \times \frac{1}{2} \times \frac{1}{2}

    So probability for exactly 2 tails for 3 coin tosses = 3 \left( \frac{1}{2} \right)^3 = \frac{3}{8}
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