Answer
$24$
Work Step by Step
The number of ways to select the second singer: $3$ (any of them can be apart from the one who wants to be the last and the already selected first singer)
The number of ways to select the third singer: $2$ (any of them can be apart from the one who wants to be the last and the already selected first and second singer)
Then the fourth singer is the one who is not the first, second, third or last.
The last singer is fixed.
Number of different ways to schedule the appearances:$4\cdot3\cdot2\cdot1\cdot1=24$
