"I have a grammar question for you. Today, my ESL 300 students (from India in particular) were confused about this sentence that I had asked them to edit.I've never come across such a notion, but a quick search of google.co.in for two third(s) of finds about 20,000 for the singular vs about 157,000 for the plural, a ratio of 1:8. Singulars appear even in headlines in newspapers, so it may actually be a feature of Indian English.
Two third of the respondents worked or had worked at properties that had websites.
They were convinced that two thirds did not need an 's'. Are there any rules for this? Or, do you think this relates to differences between Indian English and NAE? I know we would say one third, but I told them that two thirds definitely needs an 's.' Do you know why?"
In contrast, the COCA has a ratio closer to 1:100.
When you look at three quarter(s), however, the google.co.in ratio is approaching normal (1:60), so it seems as though it may be a particular fraction rather than fractions in general.
The only other related oddity that comes to mind is half, which is rather unlike all the other fractions, but it's weird in other ways. I don't have a good explanation for the lack of plural marking, but it is certainly non-standard here in Canada. The only use I can think of that might be OK would be as a modifier (e.g., a two-third majority), but even that strains credulity.