Solution: First, choose 2 phonemes from 5: $ \binom{5}{2} = 10 $. For each pair, the number of 4-phoneme words using both phonemes (but not just one) is $ 2^4 - 2 = 14 $ (subtracting the two monochromatic words). Total favorable outcomes: $ 10 \cdot 14 = 140 $. Total possible words: $ 5^4 = 625 $. Probability:

Sat, 18 Apr 2026 15:20:14 +0000

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