Use a two-dice sample space for conditional probability and construct a zero-expectation game.

Use a two-dice sample space for conditional probability and construct a zero-expectation game.

13 marks
ProbabilityQuestionBank.pdf

Two standard six-sided dice are tossed. A diagram representing the sample space is shown below. Let \(X\) be the sum of the scores on the two dice.

Second die
First die
123456
1\((1,1)\)\((1,2)\)\((1,3)\)\((1,4)\)\((1,5)\)\((1,6)\)
2\((2,1)\)\((2,2)\)\((2,3)\)\((2,4)\)\((2,5)\)\((2,6)\)
3\((3,1)\)\((3,2)\)\((3,3)\)\((3,4)\)\((3,5)\)\((3,6)\)
4\((4,1)\)\((4,2)\)\((4,3)\)\((4,4)\)\((4,5)\)\((4,6)\)
5\((5,1)\)\((5,2)\)\((5,3)\)\((5,4)\)\((5,5)\)\((5,6)\)
6\((6,1)\)\((6,2)\)\((6,3)\)\((6,4)\)\((6,5)\)\((6,6)\)
  1. Find[6]
    1. \(P(X = 6)\);
    2. \(P(X > 6)\);
    3. \(P(X = 7 | X > 5)\).
  2. Elena plays a game where she tosses two dice. If the sum is 6, she wins 3 points. If the sum is greater than 6, she wins 1 point. If the sum is less than 6, she loses k points. Find the value of k for which Elena’s expected number of points is zero.[7]

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Answer:Zero expected score requires \(3(\frac5{36})+1(\frac{21}{36})-k(\frac{10}{36})=0\), so \(k=3.6\).

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