Problem 1.
Investments. William opened two investment accounts for his grandson's college fund. The first year, these investments, which totaled $18,000, yielded $831 in simple interest. Part of the money was invested at 5.5% and the rest at 4%. How much was invested at each rate?
Problem 2.
"Arctic Antifreeze" is 18% alcohol and "Frost No-More" is 10% alcohol. How many liters of Arctic Antifreeze should be mixed with 7.5 L of Frost No-More in order to get a mixture that is 15% alcohol?
How does the author determine what the first equation should be?
What about the second equation?
How are these examples similar?
How are they different?