[tex]\begin{gathered} \text{ In this case we use the combination of C(n,k) where n is the number of cars, and k the } \\ \text{size of the group} \\ C(n,k)=\frac{n!}{k!(n-k)!} \\ \text{ So we must compute} \\ C(13,3)=\frac{13!}{3!(13-3)!} \\ C(13,3)=\frac{13!}{3!(10!)} \\ C(13,3)=\frac{13\cdot12\cdot11}{3\cdot2} \\ C(13,3)=286 \end{gathered}[/tex]
He can give the cars 286 ways