swerve wrote:Two fair die with sides numbered 1 to 6 are tossed. What is the probability that the sum of the exposed faces on the die is a prime number?
A. \(\frac{5}{11}\)
B. \(\frac{5}{12}\)
C. \(\frac{5}{21}\)
D. \(\frac{2}{9}\)
E. \(\frac{5}{36}\)
The OA is B
Source: Manhattan Prep
The prime numbers between 2 and 12, inclusive, are 2, 3, 5, 7, and 11. The possible pairings with a sum being a prime number are:
(1,1), (2,1), (1,2), (1,4), (4,1), (3,2), (2,3), (4,3), (3,4), (6,1), (1,6), (2,5), (5,2), (6,5), (5,6)
Recall that there are 36 possible outcomes from rolling two 6-sided dice. Thus, the probability that the sum is a prime number is 15/36 = 5/12.
Answer: B