## Precalculus (10th Edition)

$24$
The number of ways arranging $n$ distinct objects is $n!=n\cdot(n-1)\cdot(n-2)\cdot...\cdot3\cdot2\cdot1.$ Hence, the number of ways of arranging $4$ people in a line is: $4!=4\cdot3\cdot2\cdot1=24.$