Exam-Style Problem

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Nov 2013 p61 q7
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James has a fair coin and a fair tetrahedral die with four faces numbered 1, 2, 3, 4. He tosses the coin once and the die twice. The random variable X is defined as follows.

  • If the coin shows a head then X is the sum of the scores on the two throws of the die.
  • If the coin shows a tail then X is the score on the first throw of the die only.

(i) Explain why X = 1 can only be obtained by throwing a tail, and show that P(X = 1) = \(\frac{1}{8}\).

(ii) Show that P(X = 3) = \(\frac{3}{16}\).

(iii) Copy and complete the probability distribution table for X.

x12345678
P(X = x)\(\frac{1}{8}\)\(\frac{3}{16}\)\(\frac{1}{8}\)

Event Q is ‘James throws a tail’. Event R is ‘the value of X is 7’.

(iv) Determine whether events Q and R are exclusive. Justify your answer.

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