Question

In how many ways can 6 people be seated for group photographs if there are only 4 seats?

Answer 1

As the order of the people does matter, we need to find the number of permutations without repetition, we choose 4 people of 6:

$P(n, r) =\cfrac{n! } {(n-r)! } ;\\ P(6,4)=\cfrac{6!}{2!}=6\cdot5\cdot4\cdot3=360.$