Now that it's getting close to Halloween, we're running a contest to hear your scariest stories! These can be scary stories that you've experienced or stories that you've heard and the story with the most reactions will win!
I'd classify this kind of thing under 'low yield'. You might see it if you take 10 tests, but probability for it's own sake is rare.
You should know what these things are, but unless you're clear on everything else the MCAT tests, I wouldn't waste more time on stats problems. Oftentimes if you see these concepts, it's going to be in conjunction with other, normal science stuff in a passage.