Let n be a positive integer. Chef Kao has n different flavors of ice cream. He wants to serve one small cup and one large cup for each flavor. He arranges the 2n ice cream cups into two rows of n cups on a tray. He wants the tray to be colorful, so he arranges the ice cream cups with the following conditions: [*]each row contains all ice cream flavors, and
[*]each column has different sizes of ice cream cup.
Determine the number of ways that Chef Kao can arrange cups of ice cream with the above conditions. combinatoricsEnumerative Combinatorics