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?
A) $\$ 1200$
B) $\$ 150$
C) $\$ 120$
D) $\$ 15$

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? 
A) $\$ 1200$
B) $\$ 150$
C) $\$ 120$
D) $\$ 15$

Quizplus · Accepted Answer

First, calculate the energy used per day in kilowatt-hours (kWh). A 400-W computer uses 400 watts or 0.4 kW. Over 8 hours, it uses $0.4 \, \text{kW} \times 8 \, \text{hours} = 3.2 \, \text{kWh}$ per day. Annually, this amounts to $3.2 \, \text{kWh/day} \times 365 \, \text{days} = 1168 \, \text{kWh}$. At a cost of 10¢ per kWh, the annual cost is $1168 \, \text{kWh} \times \$0.10/\text{kWh} = \$116.80$, which rounds to approximately \$120.

A 400-W Computer (Including Its Monitor) Is Turned on for 8.0