Why was my question closed: If Alice must've have classes on at least 2 days, why do you need the intersection of 3 's?
I don't know why the MathJax isn't processing at https://math.codidact.com/posts/282645.
But why was it closed "as not constructive"?
This question cannot be answered in a way that is helpful to anyone. It's not possible to learn something from possible answers, except for the solution for the specific problem of the asker.
I'm befuddled because isn't the helpfulness and learnedness of my question obvious? "This question cannot be answered in a way that is helpful to anyone." What on earth?
Many students use this textbook, may have this same question, and will be assisted by answers.
This question makes it "possible to learn something" about the Inclusion-Exclusion Principle.