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.
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.
, 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:
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:
, where greater compressions strip away more conceptual correlation for brevity, but no one should write it as, e.g.
, 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:
, while discouraged-but-sometimes-acceptable choices include
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
, 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.