Question

four out of 9 performers will be chosen to stand in a row on stage. how many ways can the 4 performers stand in a row

Answer 1

The order matters.

`k` objects can be chosen out of
`n` objects, when the order matters, in
`P(n,k)=(n!)/((n-k)!)` ways.

So, the answer is
`P(9,4)=(9!)/(5!)=6\cdot7\cdot8\cdot9=3024` ways.