數學題,,,

2007-10-30 5:45 am
18.Suppose that we roll a pair of balanced dice, X is the number of dice that come up 1, and Y is the number of dice that come up 4, 5, or 6. Construct a table showing the values of the joint probability distribution of X and Y.
更新1:

can u explain the question for me. I don't understand the questions so that I cannot know why X and Y =0,1,2

回答 (1)

2007-11-01 8:24 am
✔ 最佳答案
The possible outcomes of throwing two dice are
(1,1) (1,2) (1,3) (1,4) (1,5) (1,6)
(2,1) (2,2) (2,3) (2,4) (2,5) (2,6)
(3,1) (3,2) (3,3) (3,4) (3,5) (3,6)
(4,1) (4,2) (4,3) (4,4) (4,5) (4,6)
(5,1) (5,2) (5,3) (5,4) (5,5) (5,6)
(6,1) (6,2) (6,3) (6,4) (6,5) (6,6)
Since we roll a pair of balanced dice, the possible values of X and Y are 0,1,2 respectively
For X=0, Y=0 suitable outcomes are
(2,2) (2,3) (3,2) (3,3)
For X=0, Y=1 suitable outcomes are
(2,4) (2,5) (2,6) (3,4) (3,5) (3,6) (4,2) (4,3) (5,2) (5,3) (6,2) (6,3)
For X=0, Y=2 suitable outcomes are
(4,4) (4,5) (4,6) (5,4) (5,5) (5,6) (6,4) (6,5) (6,6)
For X=1, Y=0 suitable outcomes are
(1,2) (1,3) (2,1) (3,1)
For X=1, Y=1 suitable outcomes are
(1,4) (1,5) (1,6) (4,1) (5,1) (6,1)
For X=1, Y=2 suitable outcome is 0
For X=2, Y=0 suitable outcome is
(1,1)
For X=2, Y=1 suitable outcome is
For X=2, Y=2 suitable outcome is 0
The joint probability distribution table of X and Y is






X/Y
0
1
2

0
4/36
12/36
9/36

1
4/36
6/36
0

2
1/36
0
0


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