I had half a semester's worth of homework to do, and a month's worth of material to learn. Over the 24 hours between 4 pm on Sunday and 4 pm on Monday, I learned 150 pages worth of math, did 15 handwritten pages worth of homework, and got an 84 on the final (and aced the extra credit questions for the first 2 midterms). I got an 80 in the class.
I raised my grade from a D to a B in 24 hours. I attended class maybe 3 times, and this was a class for junior and senior math majors.
Most colleges/Unis I know of have 60 at a D and technically that's passing (however only Cs usually transfer, and some programs will only accept grades of C or better).
At my school, D-level grades are passing only if you're using them as an elective. You can't fulfill any degree requirements unless you have a C- or better.
I did pretty much the same thing in my calc 3 class. I did nothing all semester except for the 24 hours before my tests and got a B (because I got a 68-ish on the first test because I forgot my precal and that was 3-dimensional precal)