total outcomes by rolling two dice =6² = 36
outcomes are
1,1 | 2,1 | 3,1 | 4,1 | 5,1 | 6,1 |
1,2 | 2,2 | 3,2 | 4,2 | 5,2 | 6,2 |
1,3 | 2,3 | 3,3 | 4,3 | 5,3 | 6,3 |
1,4 | 2,4 | 3,4 | 4,4 | 5,4 | 6,4 |
1,5 | 2,5 | 3,5 | 4,5 | 5,5 | 6,5 |
1,6 | 2,6 | 3,6 | 4,6 | 5,6 | 6,6 |
a single die has 6 outcomes
P(X=1) = 1/6
P(Y=1) = 1/6
P(X=1,Y=1) = 1/36
from here,
P(X=1,Y=1)=P(x=1) * P(Y=1)
similarly
P(X=2,Y=2)=P(x=2) * P(Y=2)
ans so on
so, it can be generalised as
P(X=x,Y=y) = P(X=x) * P(Y=y)
Y | ||||||||
1 | 2 | 3 | 4 | 5 | 6 | P(X=x) | ||
X | 1 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/6 |
2 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/6 | |
3 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/6 | |
4 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/6 | |
5 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/6 | |
6 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/36 | 1/6 | |
P(Y=y) | 1/6 | 1/6 | 1/6 | 1/6 | 1/6 | 1/6 | 1 |
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