1. Not finding help here? Sign up for a free 30min 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!

A question about dice probability calculation

  1. Nov 28, 2007 #1
    A question about probability calculation
    What is the probability that the sum from two dices are under 9, i don’t know a fast way to calculate that :(, instead i calculated it manually by listing all possible event.
    Divided by the total number of outcomes 6*6=36

    And something else that I can not understand,
    p=probability that this happen

    Case 1
    dice (1,1), dice (1,1), <-> is one event <-> 2p
    case 2
    dice(1,2) and dice(2,1) <-> is two events <->2p

    How come case one gets 1 event and 2p when case 2 gets two events and 2p ...

    Kindly TNS ...
     
  2. jcsd
  3. Nov 28, 2007 #2

    rock.freak667

    User Avatar
    Homework Helper

    If you get more than 9(assuming that you meant sum>9 and not equal to 9) you can get (6,3) or (6,4) or (6,5) or (6,6) or (5,5) or (5,4) <---- these gives you the possibilities to get a sum[itex]\geq[/itex]9. NOTE: this follows the order, (dice1,dice2)

    so to get (6,3)=[itex]\frac{1}{6}*\frac{1}{3}*2!=\frac{1}{9}[/itex]

    since all the possibilities will be similar to that it will simply be [itex]\frac{1}{9}*6[/itex] which is [itex]\frac{2}{3}[/itex] but this is to find P(sum[itex]\geq[/itex]9) so then to find what you want is simply 1-P(sum[itex]\geq[/itex]9)
     
  4. Nov 28, 2007 #3

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    If you were calculating the probability of getting a 2 on a pair of dice, there is only one way that can happen. Die "A" is a 1 and die "B" is a 1. Probability of rolling a 2 is 1/36.
    If you were calculating the probability of getting a 3 on a pair of dice, there are two ways that can happen. Die "A" is a 2 and die "B" is a 1 or die "A" is a 1 and die "B" is a 2. Probability of rolling a 3 is 2/36= 1/18.
     
  5. Nov 28, 2007 #4
    Thank you very much for your replies, i think it is clear now.

    Kindly TNS
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: A question about dice probability calculation
  1. Probability of a dice (Replies: 3)

Loading...