Determining Yes or No?
Octave, 29 27 bytes
Thanks to @RickHithcock for pointing out a mistake, now corrected. Also, 2 bytes off thanks to @StewieGriffin!

@(s)'yn'(mod(sum(s+1),2)+1)

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Explanation
The ASCII code point of 'y' is odd, and that of 'n' is even. The code

adds 1 to each char in the input string to make 'y' even and 'n' odd;
computes the sum;
reduces the result to 1 if even, 2 if odd;
indexes (1-based) into the string 'yn'.