Print out the following page and bring it to class with you.
A town requires a daily supply of 4 million gallons of water of a quality such that the concentration of a certain pollutant is kept below 100 mg/gallon. The water can be supplied from two sources, either purchased from a local water company at a cost of $100/million gallons, or pumped from a nearby river at a cost of $50/million gallons. The concentration of the pollutant from the water company is 50 mg/gallon, and that from the river is 200 mg/gallon. The water from the two sources is completely mixed in the town water tank before it is supplied to the customer. Determine how much water to purchase from each source.
How would you change the model if next year the River Authority tells you that the recent drought has caused your allocation to be lowered to 2 million gallons per day? What if the Well owner told you that you could only purchase a maximum of 1 million gallons per day?