Question

1) in how many ways can 5 people sit on a sofa when only 3 seats are available.
2) in how many ways can 3 people sit if there are five vacant seats.

Answer 1

1) 5P3
2) 5P3

use this formula for calculation above :
nPr = n!/(n-r)!

with n! = n(n-1)(n-2)(n-3)....3.2.1