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Math Help - Should you guess or leave it blank?

  1. #1
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    Should you guess or leave it blank?

    On a contest, there are 5 choices, you are given 2 points for leaving a question blank, and 8 points for getting an answer correct. If you had 3 questions you don't know how to do, should you leave them blank or guess? What if you had 1, 2, 4, and 5 questions blank?

    How do I calculate the probability of that and the average points you'll get for guessing?
    Last edited by chengbin; May 1st 2010 at 05:00 PM.
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  2. #2
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    Quote Originally Posted by chengbin View Post
    On a contest, there are 5 choices, you are given 2 points for leaving a question blank, and 8 points for getting an answer correct. If you had 3 questions you don't know how to do, should you leave them blank or guess?

    [snip]

    How do I calculate the probability of that and the average points you'll get for guessing?
    Let X be the random variable 'number of correct choices'.

    X ~ Binomial(n = 3, p = 1/5)

    Calculate E(X). So if you guess the answers, E(mark) = 8E(X).

    If you leave the questions blank, then you get 6 marks ....
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    Am I doing this right? I completely forgot how to do stats.

    8E(X) of B(3,1/5) = 8x3/5 = 24/5?
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  4. #4
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    Quote Originally Posted by chengbin View Post
    Am I doing this right? I completely forgot how to do stats.

    8E(X) of B(3,1/5) = 8x3/5 = 24/5?
    The answer is correct.
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