Question

choose the correct answer.
efficiency is a comparison of how much work goes into a machine versus how much work comes out of a machine. how is efficiency expressed?
in kilograms
as a percentage (%)

Explanation:

Efficiency in machines is the ratio of output work to input work. Ratios like this are typically expressed as a percentage to show the proportion of input work that becomes useful output. Kilograms are a unit of mass, not for expressing efficiency. So the correct way to express efficiency is as a percentage.

Answer:

as a percentage (%)