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Math Help - Spider Probability Problem

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    Spider Probability Problem

    A spider eats 3 flies a day. Until the spider fills its quota, it has an equal chance of catching any fly that attempts to pass. A fly is about to make an attempt. What is the chance of survival given that 5 flies have already made the attempt today?
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    Quote Originally Posted by sweeetcaroline View Post
    A spider eats 3 flies a day. Until the spider fills its quota, it has an equal chance of catching any fly that attempts to pass. A fly is about to make an attempt. What is the chance of survival given that 5 flies have already made the attempt today?
    Pr(survival) = \Pr(X = 3) \cdot 0 + \Pr(X < 3) \cdot \frac{1}{2}.

    Use the fact that X ~ Binomial(n = 5, p = 1/2) to calculate \Pr(X < 3).
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