Answer:
Robert can read the books in 129,600 different ways.
Step-by-step explanation:
The order in which the book are read is important, which means that the permutations formula is used to solve this question.
Permutations formula:
The number of possible permutations of x elements from a set of n elements is given by the following formula:
[tex]P_{(n,x)} = \frac{n!}{(n-x)!}[/tex]
Top shelf:
4 books from a set of 6. So
[tex]P_{(6,4)} = \frac{6!}{2!} = 360[/tex]
Middle shelf:
2 books from a set of 3. So
[tex]P_{(3,2)} = \frac{3!}{2!} = 3[/tex]
Bottom shelf:
3 books from a set of 6. So
[tex]P_{(6,3)} = \frac{6!}{3!} = 120[/tex]
Total:
360*3*120 = 129,600
Robert can read the books in 129,600 different ways.