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Math Help - Odds of a coin flip

  1. #1
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    Question Odds of a coin flip

    If Robbie tosses a coin 8 times, what are the odds that at least twice it will be heads??

    i know i have to do

    (1/2)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2)

    and then multipy but how would i figure out the odds of 2 heads
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  2. #2
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    Quote Originally Posted by lucifer_x View Post
    If Robbie tosses a coin 8 times, what are the odds that at least twice it will be heads??

    i know i have to do

    (1/2)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2)*(1/2)

    and then multipy but how would i figure out the odds of 2 heads
    The probability of at least two heads is 1 - (probability of less than two heads = 1 - (probability of 1 head + probability of no heads) = 1 - \left[ 8 \cdot \left( \frac{1}{2} \right)^8 + \left(\frac{1}{2}\right)^8\right] = \, .... .

    Now use the definition of odds ... (perhaps see this thread: http://www.mathhelpforum.com/math-he...y-problem.html)
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