9) For this question, we know that a device uses 1 Watt, and that electricity costs $0.10 for every kilowatt-hour. We need to use dimensional analysis to answer this question.
We should be asking ourselves the following: how can I get from Watts to kilowatt-hours? First, we would convert Watts to kilowatts. Next, we can multiply by the total hours we are measuring. Our problem specifies that we are leaving the device powered for one year, so we should convert one year to hours.
Remember that although, we find that the energy is 8.76 kilowatt-hours, we want to find how much it costs to supply that energy for the device. This is why we multiply by the rate given in the problem.
Answer: C
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