## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$24$ different ways
Lining people up involves permutation (because order matters) of 4 distinct objects taken 4 at a time. Use the formula $P(n,r)=\dfrac{n!}{(n-r)!}$: $P(4,4) \\= \dfrac{4!}{(4-4)!} \\= \frac{4\times3\times2\times1}{0!} \\= \dfrac{24}{1} \\= 24$ Thus, 4 people can line up in 24 different ways.