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Possible sums range from 2 to 12. Prime sums in this range are 2, 3, 5, 7, and 11. Count ordered pairs:

Sum 2: (1,1) → 1 way

Sum 3: (1,2), (2,1) → 2 ways

Sum 5: (1,4), (2,3), (3,2), (4,1) → 4 ways

Sum 7: (1,6), (2,5), (3,4), (4,3), (5,2), (6,1) → 6 ways

Sum 11: (5,6), (6,5) → 2 ways

Total favorable outcomes = 1+2+4+6+2=151 + 2 + 4 + 6 + 2 = 15. Total outcomes = 6×6=366 \times 6 = 36. Probability =15/36=5/12= 15/36 = 5/12. Option B is correct. This item tests discrete probability, counting, and recognition of primes—core GRE Quant skills. A common pitfall is missing symmetric pairs or including composite sums like 9 or 10. Another is forgetting that dice outcomes are ordered; (2,3) and (3,2) are distinct. When time is short, note that the distribution of sums is triangular: counts increase up to 7 and then decrease symmetrically. Knowing that 7 has 6 outcomes and using symmetry speeds enumeration. Reduce fractions to simplest terms; 15/36 simplifies by dividing numerator and denominator by 3, yielding 5/12.