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I want to start off by saying I'm not someone who is particularly strong at math, and that this is a fairly abstract question.

Today I was reading a comment on reddit, a user posted something to the effect of if you aren't sure 100000% about doing something, you shouldn't do it. I was annoyed by the percentage they used, it's obvious that you can't have more than 100% of something. (without going over the maximum quantity)

This got me thinking. Why does 100% represent the maximum value of something?

Let's say I took a test with 10 questions and got all 10 correct. I would have received a 100% on the test. Why? Why doesn't 200% or any other number represent the maximum percent that I can achieve?

I think it might be an arbitrary value chosen. It's easy to convert numbers to percentages with 100% being the maximum.

In summary, why does 1/1 = 100%? Why doesn't 1/1 = 200%, or 137.45%?

Jerred Shepherd
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    I agree with you in that it's an arbitrary choice. However, in everyday speech, the percentages are a constant object of exaggeration, so it's normal to say "Give your 110%" even though it's actually impossible. – Matti P. May 16 '18 at 05:50
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    There are of course cases where percentages greater than 100 make sense: if the economy can grow 2% in one year, then it can grow 200% in 50 years. But such percentages are dangerous; many people will fail to recognise that growing by 200% means tripling in size. Phrases like "give 110% of your best" are at best a lame joke and at worst innumerate pseudo-science. – Michael Kay May 16 '18 at 08:42
  • See also: What is mathematical basis for the percent symbol (%)? – Eric May 16 '18 at 08:51
  • "Give your 110%" can make sense if 100% means something like "giving your maximum output without stressing yourself". Then 110% just means going a little above that. – Stefan Reich May 16 '18 at 10:48

3 Answers3

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Percent literally means "per hundred", as "cent" means "hundred" in French (and, originally, Latin). Hence, "percent" means "out of 100".

100% means 100 out of 100.

vadim123
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100% means $\frac{100}{100}$ (Hundred out of Hundred). In short If an apple is divided to 100 parts and you ate 5 parts, you have eaten 5% of it. you cannot eat more than 100%.

emil
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As already said, 100% means 100 out of 100.

To me, the only two ways to read a percentage superior to 100 is :

  • An oral way of emphasizing something ("I'm 1000% sure of what I'm saying"), which is mathematically wrong.
  • Talking about a rate. If a plant measures 10cm on Monday, then 20cm on Friday, it has a 100% growth rate. But if it measures, again, 10cm on Monday and then 30cm on Friday, it has a 200% growth rate. You often see this when talking/reading about economic growth.
dlmr
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