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Use your dice and cards reference sheets to help you answer the following questions. If a single six-sided number cube is rolled twice, what is the probability that the sum is greater than 5, given that the first roll was a 3?

A. 1/9
B. 13/18
C. 2/3
D. Cannot be determined

Respuesta :

The probability is 2/3.

The probability of a sum greater than 5 given the first roll is 3 is given by 
P(sum>5|first 3)=P(first 3 and sum>5)/P(first 3)

The probability of rolling a 3 first and having a sum > 5 is 4/36 = 1/9.
The probability of rolling a 3 first is 6/36 = 1/6.

1/9÷1/6 = 1/9×6/1 = 6/9 = 2/3

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