In an orchid show, seven orchids are to be placed along one side of the greenhouse. There are four lavender orchids and three white orchids. How many ways are there to lineup these orchids?
Considering only the color of the orchids, we see that the number of lineups of the orchids is
$$
\left(\begin{array}{l}
7 \\
4
\end{array}\right)=\frac{7 !}{4 ! 3 !}=35 \text {. }
$$