How many ways can a librarian arrange 15 books on a top shelf if she has 20 books from which to pick? 20!/5! 20!/15! 15!/5!

asked Jan 26, 2018 105k views

2 votes

How many ways can a librarian arrange 15 books on a top shelf if she has 20 books from which to pick?

20!/5!
20!/15!
15!/5!

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6 votes

The correct answer is A turned this in got a 100 hoped this helped ya.

9.1k points

3 votes

Use the permutation formula
nPr = (n!)/((n-r)!)
20P15 = (20!)/((20-15)!)
20P15 = (20!)/(5!)

The final answer is choice A

Magmatic answered Jan 30, 2018