Which of the following expressions gives the number of permutations of 15 objects taken 5 at a time

Which of the following expressions gives the number of permutations of 15 objects taken 5 at a time? 

1. 15(5)
2. (15 - 5)!
3. 15!/5!
4. 15!/(15 - 5)!
5. 15!/(5!)(15 - 5!)

Answer

The correct answer is D.

The formula for calculating the number of permutations of n objects taken r at a time is n!(n - r)!.