It is refreshing to find an article with a false title that contains it's own refutation within the first five paragraphs:

"The only career in which a high school graduate can expect to continue to work on [problems with a unique correct answer] is academic research in pure mathematics"

Unfortunately for this article, the premise that mathematics is the same thing as engineering is false.

If an engineering problem does not have a unique solution, its because of complications introduced by the real world. Any engineering problem which can be well-posed as a pure math problem, does of course have a unique solution; as the author concedes.