Efficiency

Machines always waste some energy. It is how much of this energy that is wasted and how much of it that is useful that decided its efficiency.

If you put petrol in a car, the car turns the chemical energy into kinetic energy so that you can drive off. However, it also turns some of it into heat energy and sound energy - these are the wasted energies.

EFFICIENCY = (USEFUL ENERGY OUTPUT  /  TOTAL ENERGY INPUT)  X  100%

The end part where you multiply it by 100% is only to give your answer as a percentage. This bit isn't necessary.