A 400-W computer (including its monitor) is turned on for 8.0 hours per day. If electricity costs 10¢ per kWh, how much does it cost to run the computer annually for a 365-day year?

Question

A 400-W computer (including its monitor) is turned on for 8.0 hours per day.  If electricity costs 10¢ per kWh, how much does it cost to run the computer annually for a 365-day year?

BlackTom AI · Accepted Answer

To determine the annual cost, start by converting the power draw to kilowatts and then multiply by the total hours used per year.
Step 1: The computer power is 400 W, which is 0.4 kW (since 1000 W = 1 kW).
Step 2: Daily energy usage = power × time = 0.4 kW × 8 h = 3.2 kWh per day.
Step 3: Annual energy usage = 3.2 kWh/day × 365 days = 1,168 kWh per year.
Step 4: Cost = energy × price per kWh. With electricity costing $0.10 per kWh, annual cost = 1,168 kWh × $0.10/kWh = $116.8.
Rounding to the nearest dollar gives $117.
Now evaluate the other options: 
- $1200 would require roughly 12,000 kWh/year, which is far greater than 1,168 kWh, so it’s not plausible for a single 400 W device.
- $17 implies about 170 kWh/year, far below the calculated 1,168 kWh, indicating an underestimation of usage.
- $57 implies about 570 kWh/year, which is also too low compared to the actual energy consumption calculated from the given power and time.
Thus, the correct calculated annual cost is $117, and the other choices fail to match the energy usage derived from 0.4 kW for 8 hours daily over a year.

A 400-W computer (including its monitor) is turned on for 8.0 hours per day. If electricity costs 10¢ per kWh, how much does it cost to run the computer annually for a 365-day year?单项选择题

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