The typical subway station in Washington, DC$,$ has six turnstiles, each of which can be controlled by the station manager to be used for either entrance or exit control$$but never for both. The manager must decide at different times of the day how many turnstiles to use for entering passengers and how many to use for exiting passengers.The typical subway station in Washington, DC$,$ has six turnstiles, each of which can be controlled by the station manager to be used for either entrance or exit control$$but never for both. The manager must decide at different times of the day how many turnstiles to use for entering passengers and how many to use for exiting passengers.