Wu rolls two fair, six-sided dice. You are not told what the rolls were, but you are told that the sum of the two rolls is a prime. What is the probability that the sum of the two rolls is $5$?

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Answer:

The probability that the sum of the two rolls is 5 is 0.455.

Step-by-step explanation:

The outcomes of the roll of two dice are:

S = {(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6)

      (2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6)

      (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6)

      (4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6)

      (5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6)

      (6, 1), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6)}

The sum of the two numbers are in the set:

S₁ = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12} = 11 possible outcomes

The subset of prime numbers from the above set is,

S₂ = {2, 3, 5, 7, 11} = 5 possible outcomes.

Compute the probability that the sum of the two rolls is 5 as follows:

[tex]P(Sum=5)=\frac{5}{11}=0.455[/tex]

Thus, the probability that the sum of the two rolls is 5 is 0.455.

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