1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    HallsofIvy

    User Avatar
    Science Advisor

    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.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted