2022 SAJC J2 CT Q9

2022 SAJC J2 CT Q9

9 marks
Mid Year Exam

The events \(A\) and \(B\) are such that \(\mathrm{P}\left( A \right)=0.3\), \(\mathrm{P}\left( B' \right)=0.85\) and \(\mathrm{P}\left( \left. B \right|A \right)=0.15\).

  1. Find \(\mathrm{P}\left( A'\cap B' \right)\) and hence prove that the events \(A'\) and \(B'\) are independent events.[4]

A third event \(C\) is such that \(\mathrm{P}\left( C \right)=0.45\) and \(\mathrm{P}\left( A\cap B\cap C \right)=0.03\). It is also given that events \(B\) and \(C\) are independent, and that events \(A\) and \(C\) are not independent.

  1. Find the range of possible values of \(\mathrm{P}\left( A'\cap B'\cap C' \right)\).[5]

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Answer:\(A'\) and \(B'\) are independent; \(0.2125 \leq \text{P}\hspace{0.1em}(A' \cap B' \cap C') \leq 0.4675\), \(\text{P}\hspace{0.1em}(A' \cap B' \cap C') \neq 0.3125\)

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