# Math Help - Permutation or combination?

1. ## Permutation or combination?

Nine students enter a classroom with 15 desks. How many seating arrangements are possible if each student selects a desk?

p = n!/(n-r)! = 165110400 doesn't sound right

Thanks

2. Originally Posted by terminator
Nine students enter a classroom with 15 desks. How many seating arrangements are possible if each student selects a desk?

p = n!/(n-r)! = 165110400 doesn't sound right

Thanks
$\displaystyle \frac {n!}{k!(n-k)!}$

3. Originally Posted by terminator
Nine students enter a classroom with 15 desks. How many seating arrangements are possible if each student selects a desk?
p = n!/(n-r)! = 165110400 doesn't sound right
I have no idea how you got that answer. BUT
$P(15,9)=\dfrac{15!}{6!}=1816214400$

4. The other member said is a combination.

5. The other member said is a combination(at least the first formula)

6. In any normal classroom the seats are different: perhaps numbered.
The students are clearly distinct.
So this is a permutation of 15 taken 9 at a time.

7. ## thanks

always prompt and ready to help.