Is it proper to use ordinal suffixes on fractions?

I know in more formal writing, spelling out fractions is preferred (e.g. two-thirds), and in math no suffix is used, but I frequently see ordinal suffixes being used on fractions (e.g. 2/3rds), even from reputable news sources.

2/3 is already pronounced two-thirds and, to me, the addition of rds just looks weird and is certainly unnecessary.

Google turns up millions of examples:

https://www.google.com/search?q=2%2F3rds

Even legit news sources:

http://www.cbsnews.com/8301-503544_162-57369226-503544/florida-primary-exit-polls-2-3rds-say-debates-mattered/

Wikipedia has nothing to say about it:

http://en.wikipedia.org/wiki/Fraction_(mathematics)#Pronunciation_and_spelling

Is this proper English or just an undefined grey area?

Solution 1:

The very first link from OP's Google search is Wikipedia's page on the "game" Guess 2/3 of the average. This doesn't actually include the characters 3rd at all, which is what I'd expect.

Google tries to interpret search terms in the most helpful way, but in this case it unavoidably implies greater prevalence for such use of the ordinal than actually occurs.

Searching Google Books for "up to 2/3 of" returns 34900 results, as against 771 for "up to 2 3rds of" (plus another 143 for "up to 2/3rd of", which looks really odd to me).

I'd be surprised if a recognised style guide recommended this use of ordinals - but even if there were any, it's obviously very much a minority position. For what it's worth, I think it looks slightly silly.

Solution 2:

No, it is not. For example, use ¾ or three-fourths. Do not combine them, which is analogous to saying "ATM Machine" when what you mean is "ATM."