Question

You are about to invest in a 66-inch flat screen TV. These TVs come in both Energy Star and non-Energy Star models. The cost of electricity is $0.15 per kilowatt-hour, and you expect to watch TV an average of 4 hours per day.
The non-Energy Star model uses 0.5 kW (half a kilowatt). How much will it cost you per year for electricity to run this model?

If the Energy Star model uses only 40 percent of the amount of electricity used by the non-Energy Star model, how much money would you save on your electric bill over 5 years by buying the efficient model?

Answer 1

First solve the cost of running the non- energy star model  
C = ( $ 0.15 / kWh) ( 0.5 kW) ( 4 hrs /day) 365 day
C = $ 109.5 in a year  

Solving the cost of the energy star model  
C = ( $ 0.15 / kWh) ( 0.5 kW) ( 4 hrs /day) (0.4) 365 day
C = $ 43.8   Saving in 5 years

S = ( $ 109.5 - $ 43.8) 5
S = $ 328.50