Consider a refrigerator that consumes 320 W of electric power when it is running. If the refrigerator runs only one-quarter of the time and the unit cost of electricity is $0.13/kWh, the electricity cost of this refrigerator per month (30 days) is

The electricity cost of this refrigerator per month (30 days) = $7.488

Explanation:

Amount of power consumed by the refrigerator while running = 320 W

The refrigerator runs one-quarter of the time,

So, for 30 days, 30 * 24 hours, 720 hours,

The refrigerator uses 320 * 720 * (1/4) W. h = 57600 W. h = 57.6 KWh

And electricity costs, $0.13 per KWh,

That is, 1 KWh = $0.13

57.6 KWh = 57.6 * 0.13 = $7.488