A laptop has an energy efficiency of 0.18. The laptop is used for 1 hour and during this time 88.6 kJ of energy is wasted in the form of heat and sound. How much energy was the laptop supplied with over this time? Give your answer to 3 significant figures.
A 1.8 kW kettle has an efficiency of 0.92. It is used to boil 1.3 kg of water, which requires 440 kJ of energy. How many minutes does it take the kettle to boil the water? Give your answer to the nearest minute.
An LCD TV has an efficiency of 0.28. Energy is supplied to it at a rate of 110 W. If the TV is left on for 90 minutes, how much energy is wasted? Give your answer to 2 significant figures.