In defining the variables, notice that the cost is expressed per pound of the three grains. Thus, in order to calculate the total cost, we must know the number of pounds of the grains used in one serving of the cereal. Also, the numbers in Table 8.5 are expressed in units per pound of grain, so defining variables as the number of pounds of the grains makes it easier to calculate the amounts of protein, vitamin B2, phosphorus, and magnesium. We let