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Homework Help: Probability solved with expected value E(X)

  1. Mar 30, 2013 #1
    A question on a multiple choice test has 6 answers which just one is right and the other wrong.

    If the amount of the correct answer is 10 points how many points should be substracted for a wrong answer so if nobody answers randomly choosing one of the 6 answers get, on average, 0 points?

    i thinh that this problem can be solved with expected value E(X) but i am confused on how to do it
    maybe this E(X)=10*(1/6)+0*(1/6)?
  2. jcsd
  3. Mar 30, 2013 #2


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    Your "E(X)= 10*(1/6)+ 0(1/6) is almost right but: you have "0" right where you want your unknown- the number of points given for a wrong answer and the probabilty of a wrong answer is 5/6, not 1/6. And you want the expected value to be 0: 10(1/6)+ x(5/6)= 0. Solve that for x.
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