Question 409744
no. of ways to pick first book = 20 

no. of ways to pick second book = 19  ...........( except the first )

no. of ways to pick third book = 18 .......(except the first and second)

and so on........

now, total no. of ways to pick 5 books in a specific order = 20*19*18*17*16

=  1860480


another ways...


no. of ways to pick 5 books from 20 books in a specific order = 20P5 

= 20!/15!

= 1860480