2015 PJC P2 Q11

2015 PJC P2 Q11

IP 4
9 marks

For events \(A\) and \(B\), it is given that \(\mathrm{P}\left( B \right)=\frac{7}{27}\), \(\mathrm{P}\left( B|A \right)=\frac{2}{9}\) and \(\mathrm{P}\left( A|B' \right)=\frac{7}{10}\).

  1. State, with reason, whether \(A\) and \(B\)are independent.[1]
  2. Find \(\mathrm{P}\left( A\cup B \right)\).[3]
  3. Find \(\mathrm{P}\left( A\cap B \right)\).[3]

For a third event \(C\), it is given that \(\mathrm{P}\left( B\cap C \right)=\frac{1}{18}\) and that \(A\) and \(C\) are mutually exclusive.

  1. Find the range of \(\mathrm{P}\left( C \right)\).[2]

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Answer:(i) Not independent (ii) \(\frac79\) (iii) \(\frac4{27}\) (iv) \(\frac1{18}\leq P(C)\leq\frac5{18}\)

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