Light-emitting diode (led) light bulbs have become required in recent years, but do they make financial sense? suppose a typical 60-watt incadescent light bulb costs $.45 and lasts for 1,000 hours. a 7-watt led, which provides the same light, costs $2.25 and lasts for 40,000 hours. a kilowatt-hour of electricity costs $.121, which is about the national average. a kilowatt-hour is 1,000 watts for 1 hour. suppose you have a residence with a lot of incandescent bulbs that are used on average 500 hours a year. the average bulb will be about halfway through its life, so it will have 500 hours remaining (and you can’t tell which bulbs are older or newer). if you require a 10 percent return, at what cost per kilowatt-hour does it make sense to replace your incandescent bulbs today? (a negative answer should be indicated by a minus sign. do not round intermediate calculations and round your answer to 6 decimal places, e. g., 32.161616.) solution