Percentages and Averages are every day ways we work with numbers to show how good or bad something is to kind of gauge where we need to focus our attention and if something is working quite as well as expected.
Lets say something is 99% (percent) efficient, we can see that's good where as something that is 1% efficient is bad.
When do we know it needs to be replaced, well we have an average component life-cycle or average uses before it needs replacing.
So how do we find this information.
Well the following two videos, yes that guy from Math Antics - he is so fun, will show you the mechanics of these mathematical problems.
Video on Percentages
Video on Averages - Mean, Median and Mode