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 $P(n,k)=\dfrac{n!}{(n-k)!}$ ways.

So, the answer is $P(9,4)=\dfrac{9!}{5!}=6\cdot7\cdot8\cdot9=3024$ ways.