Two fair dice are thrown together. Find the probability that one die shows a multiple of 2 and the other die shows a multiple of 3 (order doesn’t matter).

Difficulty: Medium

Correct Answer: 11/36

Explanation:


Introduction / Context:
We are asked for the probability that, in a single toss of two fair dice, the pair of outcomes has one value that is a multiple of 2 and the other value that is a multiple of 3. Order does not matter, so pairs like (6,6) should be counted once overall, not twice.


Given Data / Assumptions:

  • Each die has faces {1,2,3,4,5,6} with equal probability.
  • Multiples: of 2 are {2,4,6}; of 3 are {3,6}.
  • Sample space size = 36 ordered pairs.


Concept / Approach:
Use inclusion–exclusion over the two ordered scenarios: (Die1 multiple of 2 & Die2 multiple of 3) OR (Die1 multiple of 3 & Die2 multiple of 2). Subtract the overlap where both dice show a common multiple of 2 and 3, namely 6.


Step-by-Step Solution:

P(Die1 mult 2, Die2 mult 3) = (3/6)(2/6) = 1/6.P(Die1 mult 3, Die2 mult 2) = (2/6)(3/6) = 1/6.Overlap P(Die1=6, Die2=6) = (1/6)*(1/6) = 1/36.Total = 1/6 + 1/6 − 1/36 = 12/36 − 1/36 = 11/36.


Verification / Alternative check:
Counting favorable ordered pairs directly: {2,3},{2,6},{4,3},{4,6},{6,3},{6,6} and the symmetric ones where roles swap; careful de-duplication yields 11 favorable outcomes out of 36.


Why Other Options Are Wrong:
1/3 double-counts (6,6) without inclusion–exclusion. 1/4 and 7/26 come from ad-hoc approximations, not exact counting.


Common Pitfalls:
Double-counting (6,6) because it satisfies both role assignments; forgetting that order is part of the 36 equally likely ordered outcomes.


Final Answer:
11/36

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