2024 MI P2 Q7

2024 MI P2 Q7

7 marks
Prelims

A biased \(6\)-sided die gives the score \(1\), \(2\), \(3\), \(4\), \(5\), and \(8\) with probabilities shown in the table below, where \(p\) and \(q\) are positive constants such that \(p\ne q\).

Score\(1\)\(2\)\(3\)\(4\)\(5\)\(8\)
Probability\(p\)\(q\)\(0.1\)\(p - q\)\(0.2\)\(p + q\)
  1. Explain why a score of \(1\) is more likely to happen than a score of \(2\).[1]
  2. Show that \(3p+q=0.7\).[1]
  3. Given that the mean score is \(4\), \(6\), find the variance of the score.[5]

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Answer:(i) \(p>q\) (ii) \(3p+q=0.7\) (iii) \(p=0.18\), \(q=0.16\), \(\mathrm{Var}(X)=7.64\)

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