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Discrete Random Variables

  1. Jul 31, 2004 #1
    Consider the experiment of tossing a die thrice. X is defined as the number of different faces that appear (i.e., X = 1,2,3). What is meant by the "number of different faces that appear"? Could you help me how could I get P(X = 1,2,3)?
     
  2. jcsd
  3. Jul 31, 2004 #2
    well,
    u r rolling three dice ... so u could get them all different so number of different faces u will have is 3 .... or you could get 2 same numbers but 1 different , so number of different faces u see is 2 ..... or u could get all the three numbers same which means number of different faces u see is 1.

    so X can take values 1,2 and 3.

    Now u can solve it pretty easily in two possible ways ,
    1> enumerate all possible triplets
    (1,1,1),(1,1,2),........(6,6,6).
    then simply do the counting.

    2> if you are good at combinatorics ... then u can do it faster by considering
    a. number of ways u can get all three numbers different
    b. number of ways u can get two numbers same and 1 different
    c. number of ways u can get all three numbers same

    -- AI
     
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