NCERT Class XII Mathematics Chapter - - Solutions

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Question : 11
Total: 101
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)
Solution:  
If a fair die is rolled, then the sample space is S = {1, 2, 3, 4, 5, 6}
Now, E ∩ F = F ∩ E = {3}, E ∩ G = G ∩ E = {3, 5}, E ∪ F = {1, 2, 3, 5},
(E ∪ F) ∩ G = {2, 3, 5}, (E ∩ F) ∩ G = {3}.
P(E) = 3/6, P(F) = 2/6, P(G) = 4/6, P(E ∩ F) = 1/6, P(E ∩ G) = 2/6, P(E ∪ F) = 4/6, P((E ∪ F) ∩ G) = 3/6, P((E ∩ F) ∩ G) = 1/6
(i) P (E | F) =
P(EF)
P(F)
=
16
26
=
1
2

and P(F | E) =
P(EF)
P(E)
=
16
36
=
1
3

(ii) P(E | G) =
P(EG)
P(G)
=
26
46
=
1
2

and P(G | E) =
P(GE)
P(E)
=
26
36
=
2
3

(iii) P ((E ∪ F) | G) =
P((EF)G)
P(G)
=
36
46
=
3
4

and P((E ∩ F) | G) =
P((EF)G)
P(G)
=
16
46
=
1
4
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