By installing a $120 thermostat that reduces the temperature setting at night, a family hopes to cut its annual bill for heating oil by 8 percent, and thereby recover the cost of the thermostat in fuel savings after 2 years. What was the family's annual fuel bill before installing the thermostat?
Reformulate this problem and solve it. Then go one step further and give a formula (in a and b) for the family's annual fuel bill if they install a $a thermostat and are able to reduce the annual bill by b percent.
Erich Prisner, August 2003