An energy-efficient lightbulb, taking in 25.0 W of power, can produce the same l

Question

An energy-efficient lightbulb, taking in 25.0 W of power, can produce the same level of brightness as a conventional bulb operating at power 100 W. The lifetime of the energy-efficient bulb is 10,000 h and its purchase price is $17.00, whereas the conventional bulb has lifetime 750 h and costs $0.420 per bulb. Determine the total savings obtained by using one energy-efficient bulb over its lifetime as opposed to using conventional bulbs over the same time period. Assume an energy cost of $0.0760 per kilowatt-hour.

Explanation / Answer

For 25W bulb
Energy used =25*104=250Kwh
Total cost =17+250*0.076 =$36
For 100W bulb
Energy used =100*104 =1000Kwh
Bulb usage =104/750 =13.33
Total cost =13.33*0.42+1000*0.076 =$81.6

Savings =$81.6-$36=$45.6

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