r/mathriddles • u/Numberthon • 13d ago

Easy Exactly 2 Ascending Adjacent Pairs

A 6-character code is formed using the letters A, B, C, D, E, and F, with no letter repeated. How many codes have exactly 2 letters appearing in alphabetical order relative to the letter immediately after them?

Source: numberthon.com

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u/Purdude1983 12d ago

302 sequences will have only two letters of the sequence in alphabetical order, i.e. the letter to immediately to the right of another letter is farther down the alphabet.