You shouldn't be able to just guess the answers one-out-of-four. When I was in school (not in US) there never was such a thing. You simply solve the problem and write an answer, which usually is a simple number.
I don't think any of my classmates or teachers ever figured that out. They just thought I was smart for finishing early with 100% correct. Which, in a way, I guess I was, but not the way they thought.