Before my final in economics I calculated that I needed 103% on the final to get and A in the class, but I only needed something like 65% to maintain my B.  So, I studied just enough to pass.  I ended up with an A for my overall grade.  I talked to the professor to figure out how he figured the grade; he gave me 105% on the final because I set the curve and most everyone else bombed it.  Sometimes not stressing out over a test is the way to go; I only pull off a B+ or A- when I tried.