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Small dice total given two or more even faces

Question

You throw three fair six-sided dice. Knowing that two or more of them came up even, find the probability that the three values add up to at most 77.

Short answer

13/10813/108. Mapping each die x↦7−xx\mapsto7-x swaps parity, so exactly half of the 216216 outcomes, 108108, have at least two even faces. Among those, the ones with total at most 77 are permutations of (1,2,4)(1,2,4), (1,2,2)(1,2,2), (2,2,3)(2,2,3) and (2,2,2)(2,2,2): 6+3+3+1=136+3+3+1=13.

Adapted from QuantQuestions.io; question and answer rewritten by SelfMadeQuant.com.

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