First let us see how many ways we can arrange four books. This can be done using a permutation: 4! = 4 x 3 x 2 x 1 = 24 ways Now we have to arrange them amongst the other 4 books, but lets consider them as package of 1. This will mean there are 5! ways to arrange the other 4 books. Combining the calculations gives us: 5! x 4! = 2880 different ways.
