How is the mechanical efficiency of a machine usually expressed 1. as a fraction 2. as a percentage 3. as inches or feet 4. as one of three classes

The efficiency of any contraption that uses energy to
do a job is defined as

         (amount of useful energy output) / (amount of energy input) .

In describing or talking about the efficiency f the machine,
it's most often expressed as a percentage.

It's important to notice that the output is taken to be the useful output.
Why is that important ? 
Here's a simple example:

If you use an incandescent light bulb as a source of light, then
the useful output is the light, and its efficiency is quite low.

If you use an incandescent light bulb as a source of heat, then
the useful output is the heat, and its efficiency is quite high.

Ifound this on google “two vectors are equal if they have the same magnitude and direction. they are parallel if they have the same or opposite direction. we can combine vectors by adding them, the sum of two vectors is called the resultant.” i hope this you.

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