I thought 2+2=5 until my astrophysics class in senior year at mit
Really, isn't that very simple? Why did you think that was the answer?
I didn't learn math in school very well
That's quite alright, but adults are expected to know the basic arithmetic rules. It's nothing to be ashamed about, just that you need to work a little harder.
Why do I need to do math when I already graduated?
Everyone learns at the own pace, but I believe that everyone should know at least the basics like this. It can get you really far in life, like doing your taxes or adding up suspicious charges. How about just taking an online refresher, there's plenty of videos online.