percentages

Nobody every writes it like that. First of all, if I wanted to express 66.66666666 I would just say two thirds or two out of three. It sounds really stupid to say 66 and two thirds percent.

I can't imagine a situation where anyone would need to write a number and it's accompanying fraction so precisely outside of mathbooks, which all that that special way of making fractions look so neat and nice. Microsoft Word has that too, and if you really like writing fractions you can use that to make it look all pretty. Even if you're writing some scientific report, just use the decimal equivalent of the fraction.

As a general rule nobody attaches fractions to precentages, because by definition percentages are already quite precise enough for most uses (a set of numbers from one to 100), and also if you think about a percentage of something as a fraction multiplied by 100 for ease of understanding, then it makes little sense to keep the fraction there.

Normally I would use decimal fractions like this: 55.23%.

If a number that can't be exactly expressed in decimal is truly required by the context, I would use 55 2/3%---no hyphen, just a space.

Fractions and decimals should always be written numerically, not spelled out (the possible exception is dialogue, except when it's unweildy). In scientific text, you can use the precent sign -- 66.6% -- but in regular descriptive "humanistic" text, you always write out the word "percent" -- 66.6 percent.

Hope this helps.

Saying that "Nobody every writes it like that... It sounds really stupid to say 66 and two thirds percent" sounds pretty stupid itself. People are always using such terms, for example:
http://www.lrc.state.ky.us/krs/342-00/732.PDF

For your information, there is no decimal equivalent for "two-thirds." It's not .6 or .66 or even .666666666666666666666666666666666666666666666666666.

When talking about very large numbers, the difference between 66-2/3% and 66.6% can be enormous.

Mark - I'd write 66 2/3%. This would be spoken with "and" replacing the inherent decimal, as "sixty-six and two-thirds percent." This is exactly what you were asking about, I believe. I have never seen in any scientific context a hyphen used in the middle of a percent. In numbers, hyphens only seem to get used when spelling them out. When you write a check, you spell out, for example, $151.26 as one hundred fifty-one and 26/00 dollars.

Why use percentages and fractions together? They are two different methods of expressing ratios - using both is confusing. How about just saying "2/3" or "two-thirds"?

"66.6 repeating %"?

What about: 66'-6 11/16" over centipede?

I would use the hyphen if I was typing 66-2/3% to make it more readable and clear.

On a web page there are superscript and subscript tags to make the 2/3 more readable and the hyphen wouldn't be needed. I don't know if the following will work in this comment, but here goes: 66 2/3.

Now you're into a matter of style.
Associated Press style states that percdentages should always be expressed as numerals, as in "66.6 percent." Chicago and Blue Book (legal) styles state that percentages should be expressed in written form if the number is less than 100, as in "sixty-six and two-thirds percent."
Not that anyone asked, but percent used to be two words, "per cent," which was a shortening of the original "per centile." I know, I know, TMI.

For those who don't like "two-thirds percent", what are you talking about??? People talk like that all the time. My bank account yields four and a half percent, or three and a quarter, not 4.5 or 3.25. Normal people just don't talk like that. Really now.
Oh, and if you do want to express the repeating decimal, as in 66.66 "repeating" percent, you would simply draw a line above the last 6 to signify the repeat. Here's a great bit of trivia. The line is called a "vinculum".
As for style, if you don't indicate the repetition, then it would be 66.67%, not 66.66%. Always round up if the digit beyond the last shown is 5 or greater.

Q:
When using numbers in a sentence to express a percentage, such as sixty-six and two-thirds percent, is it proper to use a hyphen between "66" and "2/3" or just a space?

A:
Well first of all there's just a space. But second of all you won't have to do 66 2/3% because It's equal to two thirds

2
-- = 66 2/3 %
3

In response to porsche:

If you are rounding numbers in a scientific setting, there are different rules to follow.

Examples (each rounded to one decimal place)

1.59 becomes 1.6
1.99 becomes 2.0
1.25 becomes 1.2
1.35 becomes 1.4
1.04 becomes 1.0
1.666... becomes 1.7

If you notice that 1.25 becomes 1.2 and 1.35 becomes 1.4, that is because 5 rounds to the even number.
Also, if you are rounding to one decimal place, you must have that place in your rounded number. 1.99 rounded to one decimal place does not become 2; it becomes 2.0.

Yes, eSeamus, that's absolutely correct. 5's are rounded down to the even preceding digit to ensure that rounding up is as likely as rounding down. This avoids statistically skewing certain data, for example, when the exact average might be important.

I chose not to mention such details because it's generally not done outside the scientific community. It wasn't really relevant to what I was trying to say and, being somewhat off-topic, would have just obfuscated by point.

Truth be told, it isn't commonly done even within the scientific community unless you're working extensively with statistics. I think you'd be hard pressed to find a scientific calculator that will round in this fashion even among the most advanced models. You likely won't find a computer, programming language, or floating-point processor that does either.

Oops, thats "...my point", not "...by point". I simply must proof-read better.

You just waste your time and energy saying 66.67% or 66 2/3rds%. Just say 'two-thirds' and you have it exactly right and most economically stated. What's not to like? State what you have to say in the shortest, most accurate mode. Period.

w

In legal we use 66-2/3% all the time in our finance contracts. So as much as it "sounds really stupid" to say it, we have to still know how to type it out. I also don't appreciate your pop-up asking to proofread my document then bullying me when I said no because it is a confidential document.
Thanks for the help...

For the most part, it is accurate that spelling out numbers is wrong. However, in legal writing (I'm a legal proofreader), often it is required that everything be spelled out exactly, with the express purpose of making sure there is no wiggle room for interpretation. Shakespeare had some thoughts about lawyers in Henry VI...