as spring approaches, the campus grounds staff is preparing to buy 500 truckloads of new soil to add around buildings and in gulleys where winter has worn away the surface. three sources are available at $220, $270, and $290 per truckload, respectively, but the soils vary in nitrogen and clay composition. soil from source 1 is 50% nitrogen and 40% clay; soil from source 2 is 65% nitrogen and 30% clay; and soil from source 3 is 80% nitrogen and 10% clay. the staff wants the total mix of soil to contain at least 350 truckloads of nitrogen, and at most 75 truckloads of clay. within the constraints on their needs, they wish to find a minimum cost plan to purchase the soil.
