2005 TJC P2

2005 TJC P2

7 marks
Prelims

Urn \(1\) contains \(5\) black balls and \(3\) red balls. Urn \(2\) contains \(4\) black balls and \(4\) red balls. An experiment is conducted in the following manner:

A fair die is tossed. If it shows \(1\) or \(2\), two balls are drawn from urn \(1\) without replacement.

Otherwise, one ball is drawn from each urn. Let \(X\) be the number of red balls drawn in one experiment.

Show that \(\mathrm{P}\left( X=0 \right)=\frac{55}{168}\).[1]

Find the probability distribution of \(X\). Evaluate the expectation and variance of \(X\).[6]

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Answer:\(E(X) = \frac{5}{6}\), \(\text{Var}\hspace{0.1em}(X) = \frac{29}{63}\)

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