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)