.
Vince has eight Algebra books and five Statistics books. He only has space for five books on the shelf.
If the first four slots are to be occupied by Algebra books and the last slot is to be occupied by
Statistics book, in how many ways can this be done?
~~~~~~~~~~~~~~
Any of 8 Algebra books at the 1st spot;
any of the remaining 7 Algebra books at the 2nd spot;
any of . . . and so on . . .
give, in all, 8*7*6*5 = 1680 permutations for Algebra books at four first slots.
Next, there are 5 choices to select a Statistic book to place it at the last, fifth spot.
It gives the ANSWER : there are 1680*5 = 8400 possible ways to arrange his books under given conditions.
Solved.