Question

From eight different books, in how many ways can any four of them be arranged side by side on a book shelf?

Answer 1

correct answer: 1,680

Answer 2

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.