Question 147

If two fair dice are thrown at random, then the probability that the sum of the digits on their faces is a prime number is

Solution

Cases when the sum of the numbers on the dice is a prime number (1,1),(2,1),(1,2),(3,2),(2,3),(6,1),(1,6),(6,5),(5,6),(4,3),(3,4),(2,5),(5,2),(1,4),(4,1)

Hence total of 15 cases out of a possible 36. Probability is 15/36 or 5/12


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