Count the number of strings of length 8 over a = {w, x, y, z} that begins with either w or y and have at least one x.

asked May 4, 2019 218k views

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$1\cdot4^3\cdot2=128$ - all starting with w or y

$1\cdot3^3\cdot2=54$ - all starting with w or y, not having any x

128-54=74 - starting with w or y and having at least one x

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