A whole number (like 5) is always 100% -- because 5 is 100% of 5.
However, if your question is something like: 5 is what percent of 10, you can do this:
Turn the problem into a fraction: 5/10
Divide the top number by the bottom: 5/10 = 0.5
Move the decimal two spaces: 50
Make that a percent, and you have your answer: 50%
This works with any number. So, say your problem is: 5 is what percentage of 25, you:
Turn the problem into a fraction: 5/25
Divide the top number by the bottom: 5/25 = 0.2
Move the decimal two spaces: 20
Make that a percent, and you have your answer: 20%
However, let me reiterate: 5, by itself, is 100%, because, by itself, it is simply 5/5.
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