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Expected values probability help

  1. Nov 16, 2011 #1
    A fair coin is tossed 3 times, and a player wins $26 if 3 tails occur, wins $13 if 2 tails occur, and loses $26 if no tails occur. If 1 tail occurs, no one wins. what is the expected value?


    i dont really understand what does the "if 1 tail occurs , no one wins. how do you set up that?

    i only set up up to ( $26*3/8) + ($13* 2/8) -(26* 4/8) how do i set up the if 1 tail occurs?
     
  2. jcsd
  3. Nov 16, 2011 #2

    Stephen Tashi

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    Use $0 for the winnings.

    Your probabilities add up to more than 1, so they are wrong.
     
  4. Nov 16, 2011 #3
    if i use 0 for the winnings that 1 tail occurs that just means i add 0 to the end of my equation?
    ($26*3/8) + ($13* 2/8) -(26* 4/8) + 0 (1/8)

    isnt that still the same?
    so what is wrong with my equation?
     
  5. Nov 16, 2011 #4

    Stephen Tashi

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    Yes. The zero just shows a grader than you know what you are doing.

    You have computed the probabilities incorrectly. For example, the probability of getting 2 heads in 3 tosses isn't 2/8. Of the 8 possible results of tossing 3 coins, there are 3 possible ways that one can get 2 heads and 1 tail.
     
  6. Nov 16, 2011 #5
    oh wow, i can't believe i made such a stupid mistake, thank you for helping me out
     
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