A permutation is an arrangement in which order is important. The notation for
permutations is P(n,r) which is the number of permutations of "n" things if only "r"
Example: If nine students take a test and all have different scores, the highest
score could be achieved by any of the nine students. The second highest score could
be achieved by one of the remaining 8 students. The third highest score could be
achieved by one of the 7 remaining students.
The number of possible permutations would be: P(9,3) = 9*8*7 = 504 possible arrangements
of the top three scores.