Practical Mathematics K12Leslie Green asks:

Suppose the light bulb in your fridge uses 1 Watt when on and you pay 10 cents = $0.1 per kWh.

Estimate the cost due to a faulty door switch, which keeps the light on over a 10 year period even with the fridge door closed.

(1 kWh is 1000 Watts for 1 hour)