One of each face before the two of hearts

A standard 5252-card deck is shuffled and dealt one card at a time until the 22\heartsuit appears. What is the probability that exactly one King, exactly one Queen, and exactly one Jack appear before the 22\heartsuit?

Show hints (2)+
  1. Only the 22\heartsuit and the 1212 face cards matter. First: probability exactly 33 faces precede the 22\heartsuit is 1/131/13 (its position is uniform among 1313).
  2. Then those 33 are a random 33-subset of the 1212 faces; chance of one each is (41)3/(123)\binom41^3/\binom{12}{3}.

Answer

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0.0224 (± 0.001)

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Asked at: Jane Street, Citadel

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