You are in college and picked a couple of classes for this semester. You wonder which classes you should drop, if any. 25% of classes suck and should be dropped. If a class sucks, the professor is kind of an idiot 70% of the time. Regardless of whether their classes suck or not, 20% of professors are kind of idiots. You are in a class and observe that the professor is kind of an idiot. What is the posterior probability that the class is going to suck (and ought to be dropped)?