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Nov 2014 p61 q3
2619
Jodie tosses a biased coin and throws two fair tetrahedral dice. The probability that the coin shows a head is \(\frac{1}{3}\). Each of the dice has four faces, numbered 1, 2, 3, and 4. Jodie’s score is calculated from the numbers on the faces that the dice land on, as follows:
if the coin shows a head, the two numbers from the dice are added together;
if the coin shows a tail, the two numbers from the dice are multiplied together.
Find the probability that the coin shows a head given that Jodie’s score is 8.
Solution
To find the probability that the coin shows a head given that Jodie’s score is 8, we use conditional probability:
\(P(H | 8) = \frac{P(H \cap 8)}{P(8)}\)
First, calculate \(P(8)\):
\(P(8) = P(H \text{ and } 4+4) + P(T \text{ and } 2 \times 4) + P(T \text{ and } 4 \times 2)\)