Examples on counting permutations
How many 3-letter words are possible where no letter is repeated?
P(26,3) = 26 ? (26-1) ? (26-2) = 26 ? 25 ? 24 = 15600
Suppose I have decided to give an A to exactly one student, and A-
also to exactly one student. The rest will receive B+ or lower.
How many choices do I have in the class of 15 students?