<p>Depends on course. A lot of your required or popular lecture courses will have several hundred; a senior math course may only have ten; many of your upper level courses in a major may have from 20 to 40.</p>
<p>Ditching: most professors do not take attendance and don’t care if you ditch. Since ditching classes is the number one cause of students getting low grades and flunking or dropping out, the professors don’t care if you do that either. Also, a hint: many professors have a tendency to include in their lectures a lot of things that are not in the books, and guess what most of the test is on?</p>