Evaluation of Different-Life Alternatives 5. An undergraduate engineering student and her husband operate a pet sitting service to help make ends meet. They want to add a daily service of a photo placed online for pet owners who are traveling. The estimates are equipment and setup cost $950; net monthly income over costs $70. Over a period of 3 years, will the service make at least 12 % per year compounded monthly? Solution: Interest rate of 12 % per year compounded monthly is 1% per month. Evaluation of Different-Life Alternatives 6. Heidleman Industries is considering two types of materials for roofing its warehouses. EPDM is an elastomeric polymer synthesized from ethylene, propylene and a small amount of diene monomer, compounded with carbon black, processing oils and various cross-linking and stabilizing agents. The 75-mil thickness will cost $4.10 per square foot and will last for 25 years. A thin sheet aluminum roof will cost $6.00 per square foot, but it will last for 50 years. Using an interest rate of 10 % per year and a present worth comparison, determine whether the company should install the polymer or the aluminum roof