2021 EJC P2 Q6

2021 EJC P2 Q6

7 marks
Prelims

For events \(A\) and \(B\) it is given that \(\mathrm{P}\left( A \right)=\frac{3}{5}\), \(\mathrm{P}\left( A\cap B \right)=\frac{7}{60}\) and \(\mathrm{P}\left( \left. A' \right|B \right)=\frac{13}{20}\).

  1. Show that \(\mathrm{P}\left( B \right)=\frac{1}{3}\).[3]

For a third event \(C\), it is given that \(\mathrm{P}\left( C \right)=\frac{3}{10}\) and that \(\mathrm{P}\left( B\cap C \right)=\frac{1}{10}\).

  1. Determine if events \(B\) and \(C\) are independent.[1]
  2. Given also that \(\mathrm{P}\left( A\cap B\cap C \right)=\frac{1}{15}\), find the greatest and least possible values of \(\mathrm{P}\left( A\cap B'\cap C \right)\).[3]

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Answer:(ii) \(B\) and \(C\) are independent; (iii) Greatest \(= \displaystyle\frac{7}{30}\), Least \(= 0\)

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