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Question
The probability that a student will pass the final examination in both English and Hindi is 0.5 and the probability of passing neither is 0.1. If the probability of passing the English Examination is 0.75. What is the probability of passing the Hindi Examination?
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Solution
Let A and B be the events of passing English and Hindi examinations, respectively.
Accordingly, we have:
P(A and B) = 0.5
P(not A and not B) = 0.1 [i.e. P(A' ∩ B') = 0.1]
P(A) = 0.75
Now, P(A∪B) + P(A' ∩ B') = 1
⇒ P(A∪B) = 1 - P(A' ∩ B')
= 1 -0.1 = 0.9
By addition theorem, we have:
P(A ∪ B) = P(A) + P(B) - P(A ∩ B)
⇒ 0.9 = 0.75 + P (B) - 0.5
⇒ P(B) = 0.9 - 0.75 + 0.5
⇒ P(B) = 0.65
Thus, the probability of passing the Hindi examination is 0.65.
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