The ratio of output work to input work expressed as a percent is the blank of a machine.

EFFICIENCY

Explanation:

Efficiency of a machine is commonly defined as the ratio of output work (work done by the machine) to work done on the machine (input work) expressed as percent.

The efficiency of a machine offers insight on the level of energy preserved or giving out (lost) in a process.

If we examine a machine subjected to the level of work acted on it. Then the work acted on machine should be W.

The machine does its work as a result of the effort used on it to give the expected outcome. Then, the output formed by the machine should be W' .

Therefore,

The efficiency of the machine is evaluated as -

Efficiency

= work output (W)

× 100 

work input (W)                

weathering is the answer.