What’s the difference?
    • Permutation (order matters): Arrangements where the sequence is important.
       Use when Slot 1, Slot 2, … are distinct (e.g., Monday 8am ≠ Tuesday 10am).
    • Combination (order doesn’t matter): Selections where only the set of chosen items matters.
       Use when you just need a group (e.g., any set of 4 courses, regardless of times).
    Formulas
    Permutations without repetition: P(n,k) = n × (n−1) × … × (n−k+1) = n!/(n−k)!
    Combinations: C(n,k) = P(n,k)/k! = n! / (k!(n−k)!)
    How this page uses them
    • Toggle Order matters = ON → we count P(n,k) (choosing courses into distinct time slots).
    • Toggle Order matters = OFF → we count C(n,k) (just picking any set of k courses).