Arci, good to see you! I appear to have inherited your mantle as Rob's most beloved poster, only he wants me to put my driver's license online. That'll be the day. At least he believed you were you!
Anyway, arci and I disagree on this, as it is the responsibility of the writer to make clear the math of the answer. If the way a question is written leads a large number of reasonably educated readers to the wrong answer, then the writer is more at fault than the reader. Math may be about finding the correct answers, but writing is about making the correct answers understandable.