Looks like you guys didn't read the whole story. The professor specifically asked the class not to search online. The goal of the homework was to get the students to teach them to think through the puzzle.
ETA: Or, charitably, you didn't recognize that the big UPDATES at the top of the blogger's post indicate that since my original post, he thought to clarify the context and indicate that he'd actually misremembered the phrasing of the question.
Or maybe both?
I wouldn't consider the actual professor's question from the linked exam to be entrapment, as it happens. That in mind, I'll save my disgust for the people who thought the scenario of entrapment originally described was so terribly clever.