A fair die is rolled. Consider events E = {1,3,5}, F = {2,3} and G = {2,3,4,5}
Find
(i) P(E|F) and P(F|E)
(ii) P(E|G) and P(G|E)
(iii) P((E ∪ F)|G) and P ((E ∩ F)|G)
The sample space for the given experiment will be:
S = {1, 2, 3, 4, 5, 6}
Here, E = {1, 3, 5}, F = {2, 3} and G = {2, 3, 4, 5} ……….(I)
……….(II)
Now, E ∩ F = {3}, F ∩ G = {2, 3}, E ∩ G = {3, 5} ……….(III)
……….(IV)
(i) We know that
By definition of conditional probability,
[Using (II) and (IV)]
Similarly, we have
[Using (II) and (IV)]
(ii) We know that
By definition of conditional probability,
Similarly, we have
(iii) Clearly, from (I), we have
E = {1, 3, 5}, F = {2, 3} and G = {2, 3, 4, 5}
⇒ E ∪ F = {1, 2, 3, 5}
⇒ (E ∪ F) ∩ G = {2, 3, 5}
……….(V)
Now, we know that
By definition of conditional probability,
[Using (II) and (V)]
Similarly, we have E ∩ F = {3} [Using (III)]
And G = {2, 3, 4, 5} [Using (I)]
⇒ (E ∩ F) ∩ G = {3}
……….(VI)
So,
[Using (II) and (VI)]