If the 10 books are all different, we have:
• 10 ways of selecting the first book,
,• 9 ways of selecting the second book,
,• 8 ways of selecting the third book,
,• 7 ways of selecting the fourth book.
The total number of ways to arrange 4 of the 10 books is:
Answer
There are 5040 ways of arranging the books.