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Sarah rolls two fair number cubes, each labeled 1 through 6. What is the probability of rolling a sum of 7?

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Answer: The probability is 1/6.

Explanation:

If two dice are rolled together, the sample space of outcomes is

(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)

⇒ Total number of outcomes(sample space) = 36

Getting the sum 7 (favourable outcomes) = (1, 6), (2, 5), (3, 4), (4, 3), (5, 2), (6, 1).

⇒ Probability of Getting a sum 7 = Number of favourable outcomes / Total number of outcomes.

⇒ P = 6 / 36

⇒ P = 1 / 6

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