Question
Two students Anil and Ashima appeared in an examination. The probability that Anil will qualify the examination is 0.05 and that Ashima will qualify the examination is 0.10. The probability that both will qualify the examination is 0.02. Find the probability that only one of them will qualify the examination.

Answer

Let E and F be the events that Anil and Ashima will qualify the examination, respectively.
Given that
P(E) = 0.05, P(F) = 0.10 and P(E $\cap$ F) = 0.02.
The event only one of them will qualify the examination is same as the event either (Anil will qualify, and Ashima will not qualify) or (Anil will not qualify and Ashima will qualify) i.e., E $\cap$ F´ or E´ $\cap$ F, where E $\cap$ F´ and E´ $\cap$ F are mutually exclusive
Therefore,
P(only one of them will qualify)
= P(E $\cap$ F´ or E´ $\cap$ F)
= P(E $\cap$ F´) + P(E´ $\cap$ F) - P [(E $\cap$ F´) $\cap$ P(E´ $\cap$ F)] [by general addition rule and also P [(E $\cap$ F´) $\cap$ P(E´ $\cap$ F)]= 0]
= P (E) – P(E $\cap$ F) + P(F) – P (E $\cap$ F)
= 0.05 – 0.02 + 0.10 – 0.02 = 0.11

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