The same 20 days, two different calculations
With 20 days left before an exam, two questions need answering at once: how many of the remaining classes must still be attended, and how many hours a day need to go toward studying the syllabus. Both calculations use that same 20-day window, but for entirely different purposes.
What the attendance side requires
Starting at 60 out of 100 classes attended, with 20 remaining and a 75% requirement: the total classes by the end will be 120, and 75% of that is 90 — needing 30 more attended classes, but only 20 remain. The target isn't achievable even attending every single one, so the calculator shows zero classes can be missed for the rest of the term.
What the study-time side requires
For that same 20-day window, needing 120 total hours of study works out to 120 ÷ 20 = 6 hours per day (42 hours a week) — a substantial daily commitment on top of a full, unmissable class schedule.
Why this combination is the real crunch
With zero flexibility to skip class for extra study time, the full 6 hours a day has to come from outside class hours entirely — evenings, mornings, or weekends. Neither calculator alone reveals this crunch: the attendance figure alone doesn't say anything about study hours, and the study-time figure alone doesn't say anything about how much of the day is already locked into mandatory class attendance. Looking at both together is what actually shows whether a schedule like this is realistic.