A standard dice is tossed twice. What is the probability of obtaining exactly one 5? Express your answer as a common fraction.

  5/18

Step-by-step explanation:

There are a couple of ways to look at this.

1) If you make a matrix of all possibilities, you find there are 36 possible outcomes from the roll of a die twice. (That is the same number as for rolling two dice once.) Of those 36 outcomes, 10 are outcomes in which a 5 shows exactly once: (5, 1), (5, 2), (5, 3), (5, 4), (5, 6), (1, 5), (2, 5), (3, 5), (4, 5), (6, 5).

The probability of obtaining exactly one 5 is 10/36 = 5/18.

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2) As listed above, there are two ways to get exactly one 5 in two rolls:

  (5 on the first, non-5 on the second) or (non-5 on the first, 5 on the second)

When the rolls are independent, as we assume here, the probability of a certain sequence is the product of the probabilities of the events in that sequence.

  P(5, non-5) = (1/6)(5/6) = 5/36

  P(non-5, 5) = (5/6)(1/6) = 5/36

The probability of obtaining either event is the sum of their individual probabilities:

  P({5, 5'} or {5', 5}) = 5/36 +5/36 = 10/36 = 5/18

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The probability of obtaining exactly one 5 in two rolls of a die is 5/18.

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step-by-step explanation:

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