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Probability that a two is thrown

  1. Aug 18, 2009 #1
    1. The problem statement, all variables and given/known data
    A die is based so that the numbers 5 & 6 appear 3 times more often than the numbers 2 , 3 & 4. Calculate;
    i)The probability that a two is thrown.
    ii)The probability that two consecutive throws are > or equal to 10.

    3. The attempt at a solution

    Well I wasn't sure how to go about this so i imagined all of the outcomes;

    5 5 5 6 6 6 2 3 4 , satisfies the criteria meaning a 2 would be 1/9, however i have a feeling that that's nonsense...:S

    Then for ii) Combo's are 46 64 65 56 55 66 so (4 * 1/9) + (2 * (3/81) = (36/81+6/81) = (42/81)?

    I don't know how to go about these questions, sorry for bugging everyone >.<
     
  2. jcsd
  3. Aug 18, 2009 #2

    jgens

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    Gold Member

    Re: Probability

    Well, here's another way of looking at (i) . . .

    Let x be the probability that you roll a 2, then the probability that you roll a 3 or a 4 is also x and the probability that you roll a 5 or 6 is then 3x. We know that the sum of the probabilities of each possible outcome must be 1 so x + x + x + 3x + 3x = 9x = 1. Therefore x = 1/9.
     
  4. Aug 18, 2009 #3
    Re: Probability

    Please clarify:

    Did you mean to say "a die is biased so that..."?

    Does the die really have five sides (such dice do exist) or is it that this is a normal six-sided die with repeated markings?

    What is the probability of rolling a 1 if this is in fact a classically marked six-sided die?

    Without this information, the question may not be answerable.

    --Elucidus
     
  5. Aug 19, 2009 #4
    Re: Probability

    sorry, yeah, having a 1 is impossible, i think it just means it's a wierdly shaped dice or something :S

    edit: and thanks jgens that's a much simpler and better way of looking at it >.<
     
  6. Aug 19, 2009 #5
    Re: Probability

    jgens has explained the first part. In order to answer the second part, you need to determine how the two dice might have a sum >= 10 and find the probability that those results could occur.

    --Elucidus
     
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