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"9 out of 10" is mainly shortened as 9/10 in English as far as I know. In my native language (Hungarian) 10/9 is also used, although it is not as common nowadays as 9/10. Probably because the translation of "9 out of 10" in Hungarian is "10-ből 9", notice the change in the order.

Is 10/9 used in English (even if rarely) as well, and if yes then what is the reason behind it in English?

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    reminds me of the dog rates twitter account. This scores every dog in a scoring system out of 10. And always gives higher than 10. Leading to the "good dogs brent" meme – Martin Smith May 4 at 14:32
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    "Ten out of nine statistics are made up on the spot." – Abraham Lincoln. – Mazura May 4 at 18:25
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    @Mazura: just that Hungarian has noun endings instead of prepositions. -ból doesn't mean outside, don't trust Google Translate. It literally simply means "out of 10, 9" that could be said in English as well, and it would be correct even if not that idiomatic. The same applies in Hungarian, you could say "9 a 10-ből" just as well. English needs a comma, Hungarian needs a definite article when inverted. – Gábor May 4 at 22:05
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    Yeah, this happens in other languages, but not English. For example, in Chinese we say (literally translating) "10 parts, 9 of" – Quintec May 5 at 2:49
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    Are you absolutely positive this is a fraction? It could be a date, where 10/9 means the tenth day of the ninth month for most of the world, but some countries flip the order so 10/9 means ninth day of tenth month. – Criggie May 5 at 20:44
10

Is 10/9 ever used to mean “9 out of 10”?

tl;dr No. Fraction notation is a matter of mathematical symbolism, not English, and shouldn't ever be written like that in any language.


History: Fractions

Historically, folks counted with numbers: 1, 2, 3, 4, etc..

Then they figured that you could have fractions, with various ways of writing these. The history's mixed, but in short the ancient Egyptians had "unit fractions" which were basically all 1/y, e.g. 1/2.

The modern notation where we write one number over the other, e.g.

  7
-----
 100

, is often attributed to "The Book of Calculation", by Fibonacci back in 1202.

While Fibonacci appears to have kept the fully expanded form, folks who want to compact it can write it in the following ways:

  • 7/100

  • 7/100

  • 100\7

  • 100\7

Note that the latter forms, which use a backslash (\), are uncommon. They're allowed in some venues, e.g. in MATLAB (compare: 7/100 vs. 100\7), though they're generally discouraged.

This is analogous to how chemical formulae are compressed. For example, butane is already compressed (from a space-filling model) when written in text-format as

    H   H   H   H
    |   |   |   |
H - C - C - C - C - H
    |   |   |   |
    H   H   H   H

, then can be compressed to:

  • CH3CH2CH2CH3

  • C4H10

  • CH3CH2CH2CH3

  • C4H10

, where greater compressions strip away more conceptual correlation for brevity, but no one should write it as, e.g.

  • 4C10H

, because that means something different.

Point being, the syntax has meaning; aspects of it can be vary, but some variants, like writing 100/7 instead of 7/100, are objectively wrong in that they deviate from the underlying concept without any reason.


Summary: Acceptable forms.

So if you want to write "9 out of 10" as a fraction, then the decent choices might be:

  1.   9
    -----
     10
    
  2. 9/10

  3. 9/10

, while discouraged-but-sometimes-acceptable choices include

  1. 10\9

  2. 10\9


Discussion: Debates about inlining fractions.

Just to warn you, even mathematicians have differing opinions about how to best format fractions.

For example, some folks don't like using compressed formats; they always do the full

 1
---
 2

, like in "The Book of Calculation", while others strongly prefer inline formatting in nested scenarios. Plus there can be a lot of concern about doing the formatting just right (e.g., 1; 2).

Not going further into this topic here, just wanted to note that it exists.

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    "Fraction notation is a matter of mathematical symbolism, not English, and shouldn't ever be written like that in any language." But 9/10 is not necessarily fraction notation. "Nine out of ten" is not the same thing as "nine tenths," even though they are equivalent ratios. Nor is math notation universal (try "1,001" in France vs. USA). Broad generalizations about "any language" are almost guaranteed to be wrong. – LarsH May 5 at 21:11
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    "Is 10/9 ever used to mean “9 out of 10”? tl;dr– No." followed by "Summary: Acceptable forms. 5. 10\9" Strange answer. To me that read as "No, but Yes." – Dan Rayson May 6 at 4:25
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    This use of / in 10/9 to mean "10-ből 9" in Hungarian is probably more akin to using it in w/o to mean "without" in English, i.e. as an abbreviation symbol, than to its mathematical use. – walen May 6 at 6:33
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    @DanRayson There is a difference: The "no" part uses a forward slash. The "yes" part uses a backslash. So, there is no contradiction. – I'm with Monica May 6 at 6:56
  • This answer - and indeed all the disacussion on this page - really just confuses a trivial question – Fattie May 6 at 13:33
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10/9 is never used in English to mean 9 out of 10

9/10 is used because the "/" sign means divide and if you get 9 points out of 10 (9/10) then you have a score of 9 divided by 10 (which is 0.9) or 90% (i.e., multiply by 100 %, which is equivalent to 1)

Sometimes, you see a larger number first (e.g., 10/9), but this still means 10 out of 9. This occurs in the less common case where bonus marks are given and it is possible to get more than 100% on (e.g., high school tests or assignments when a bonus question is sometimes available, usually testing more advanced thinking). to reiterate, 10/9 means 10 (points scored) out of 9 (points available if you did all the questions right, excluding the bonus).

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    Could be used in a very different sense though: 10/9 = October 9th or September 10th. But really, no, we wouldn't even write dates like that except in a few special cases. – AIQ May 3 at 22:29
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    Occasionally, / is used to mean ‘or’. But that's extremely unlikely here, as it's not generally used that way with numbers (due to the confusion with ‘out of’ or division). (Also, in that case, you'd expect the lower number first.) – gidds May 4 at 13:04
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    @gidds: You would expect the lower number first, but not exclusively so, e.g. when you're trying to retain a respective order: "If you have a car that seats 6 and you travel with 2/3/4 friends, you'd have 3/2/1 empty seats in your car while travelling" (it's a silly example but the only one I could think of). – Flater May 4 at 14:56
  • @Flater but if you were to write "a million to one" using symbols it would be $1,000,000:1$ (and technically it has a $1/1,000,001$ chance of happening, as odds like this mean the ratio of unsuccessful to successful outcomes, not the ratio of successful to total). – Especially Lime May 4 at 14:57
  • @EspeciallyLime: You're mathematically correct, but my point was the inversion, not the literal number values. – Flater May 4 at 14:58
2

Is 10/9 used in English (even if rarely)?

Numerically? No, not as far as I'm aware.

The only use case I can think of is when describing ratios, e.g.:

"There's a million to one chance that I can outrun Usain Bolt"

Here, I am stating that the odds of me running faster than Usain Bolt are 1/1,000,001 (though it's generally understood to mean 1/1,000,000 since mathematical precision isn't the main focus of the statement).

As you can see, the divisor is mentioned first, even though the fraction, when written numerically, puts the divisor last.

Since fractions and ratios can be converted from each other (a to b <=> b/(a+b)), a fraction can be expressed with the divisor up front if you express it as a ratio.

Especially with "... to one" ratios and when dealing with a non-mathematical context, it's more common for "X to one" and "1/X" to be synonymous, even though that's not mathematically correct.


Note that "a million in one" is a similarly used turn of phrase, but I'm not going into the subtle distinction between the two. More information here.

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    Isn't "a million to one" expressing a ratio? It would be written 1,000,000:1. – wjandrea May 4 at 16:53
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    @wjandrea That actually agrees with this answer. 1,000,000:1 odds is the same as saying your chances are 1/1,000,001, since it would mean there are a million ways to fail and only one to succeed, so 1 out of every 1,000,001 times you would expect to succeed. – JMac May 4 at 18:09
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    Right, a horse with 2:1 odds (or 2-1 odds, or 2-to-1 odds) has a 1 in 3 chance of winning. That extra 1 in the denominator doesn't matter much for million-to-one, but it will if you're betting at the track. – Nuclear Hoagie May 4 at 19:39
  • @JMac I understand they're mathematically equivalent, but they're expressing different things. You would say the fraction as "one in a million and one", not "a million to one". Or to go with Nuclear's example, "one in three", not "two to one". – wjandrea May 5 at 4:06
  • This answer is complete bs. That's not a fraction you've expressed, it's a ratio. When writing the odds for example "one-in-a-million", the dividend comes first. When pronouncing the fraction too "one over a million" the dividend comes first. And also your answer itself "No, not as far as I'm aware" is wrong, bc "10/9" does appear in English, it just doesn't have the same meaning as the OP asker is wondering about. – theonlygusti May 5 at 8:09
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I see 10/9 meaning "9 out of 10" every day playing FORGE OF EMPIRES. When you try to build a building in the Guild Battleground you should spend some goods, and as you can see in the screenshot the formula is X/Y, where X is how many goods you have and Y - how many you are to spend.

Screenshot

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    I wouldn't necessarily read it like that...I interpret the first line, e.g., as "631 owned out of 34 needed." – Cristobol Polychronopolis May 4 at 19:59
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    If you read it normally, e.g. as 631/34, then it shows how many times you can pay that fee (e.g., 631/34 is 18 plus change, meaning that you could pay it 18 times and have some left over). If you read it flipped, then it shows what portion of your resource total it'll consume (e.g., 34/631 shows that it'll consume about 5.4% of your... gold, it looks like?). So while I could see why you might be interested in the flipped value (the reciprocal), that's not really what the notation itself means so much as a transform you happen to find useful. – Nat May 5 at 3:29
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    Just to note it, there's a third interpretation in which the slash is just a separator between the two values, e.g. like the slash in "and/or", rather than being a division symbol. Since it seems likely that folks would find it strange to see ÷ there, e.g. 631÷34, I'd probably lean toward this interpretation. (That, plus some of the fractions that could be reduced aren't, which would be weird if they were actually meant as fractions.) – Nat May 5 at 3:35
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    Nat's interpretation is the correct interpretation. This is purely stylistic and far from standard English. If it's informative for anyone, neither the game's publishing company nor none of its developers are native English. – theonlygusti May 5 at 8:14
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    Even if we assume that your analysis is correct, people should not base their understanding of English on a mobile game. This is not a good or authoritative source for English conventions – Kevin Wells May 5 at 22:23

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