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Math Help - 100 coin flips, variance?

  1. #1
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    100 coin flips, variance?

    Hello,
    I'm studying for a test and came across a problem that I am having a hard time arriving at the correct answer. The question is :Let X represent the number of heads in100 coin flips of a fair coin. The variance of X is? I know the answer to be 25, but I cannot arrive at this answer. I tried messing around with something like P(X = 100) bin(100,0.5) and then using something like variance = np(1-p) but its not working right. Any help is greatly appreciated so I can understand better, thanks!
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  2. #2
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    Quote Originally Posted by Mahonroy View Post
    Hello,
    I'm studying for a test and came across a problem that I am having a hard time arriving at the correct answer. The question is :Let X represent the number of heads in100 coin flips of a fair coin. The variance of X is? I know the answer to be 25, but I cannot arrive at this answer. I tried messing around with something like P(X = 100) bin(100,0.5) and then using something like variance = np(1-p) but its not working right. Any help is greatly appreciated so I can understand better, thanks!
    np(1-p)=100(.5)(.5)=25

    Problem?
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