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GATE CSE 2026 Session 2 Q10: Probability that the sum of two dice rolls is prime

Question

An unbiased six-faced dice whose faces are marked with numbers 1, 2, 3, 4, 5, and 6 is rolled twice in succession and the number on the top face is recorded each time. The probability that the sum of the two recorded numbers is a prime number is ________

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Answer: C (official GATE 2026 final answer key)

Concept used: Count favourable outcomes among the 36 equally likely ordered pairs.

First step: The possible prime sums are 2, 3, 5, 7 and 11; count the ordered pairs giving each.

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Source: official GATE 2026 Session 2 CS question paper and final answer key, organised by IIT Guwahati. Question paper · Answer key

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