If I don't know, Let's find out as a class

Many a time, as a student I asked a question, and if the instructor did not know they blew it off like it was not important. I believe in just the opposite; if I don't know the answer I use it as an opportunity for the class to find out the answer. Maybe I would assign them to research the topic and tell the class about it at a later date; or I would research the question myself and get back to the class as a whole.