A mine sends ore to the surface in small and large wagons. A small wagon hold 20 units of ore while a large wagon holds 50 units of ore. To avoid taking up too much space on the ramps, the number of small wagons must be at least twice as much as the number or large wagons. In addition, at least 10 large wagons must be used. If 2000 units of ore need to taken to the surface, minimize the total number of wagons needed.