How change percentile to percentage

This is rather vague. Do you have a particular problem in mind?

A percentile is a comparison of how one individual compares against others.

i.e. Suppose you took a test and scored in the 90th percentile. This means you scored as high or higher than 90% of those who took the test or scored in the top 10%. The percentage who scored higher than this would depend on how many took the test and what the scores were.

Here is an example of a percentile.

Suppose you took a civil service exam with a mean score of 75 and a standard deviation of 8.5. You have to place in the top 5% in order to be considered for employment.

This means you have to score in the top 5% or be in the 95th percentile.

x={\mu}+z\sigma

x=75+1.645(8.5)

x=89

You have to score at least an 89 to be considered.

Does that clear ti up any?