Related topic "two and two is/are four": see page 921-922 here.
two thirds (equal / equals) thirty-three point thirty-three.
If I think of the fraction 2/3, then I see it as a singular figure, and would say, "two thirds equals nought point six six (recurring).
On the other hand, I think that I would say, "One third equals nought point three three (recurring); two thirds equal nought point six six (recurring)". In that statement I would feel a change from singular to plural.
I am not sure whether this is standard BrE practice or personal idiosyncrasy.
What would you say in these two situations?
- Two-thirds is yours.
- Meaning, that fraction is yours.
- Two-thirds are yours.
- Meaning, two parts are yours.
Are they both grammatical? Yes. The pattern learners are taught (see below) is based on the presence of a noun:
- singular verb with mass nouns
- plural verb with plural nouns
- singular or plural verb with collective nouns
When the noun is left unstated, however, is where learners run into problems:
- Two-thirds of the milk is yours.
- Two-thirds of the cookies are yours.
- Two-thirds is/are yours.
As for me, I prefer this explanation: Singular or plural verb with numbers, percentages and fractions - Topic
***** NOT A TEACHER *****
(1) The teachers seem to be telling us that either singular/plural is
"correct" -- depending on what you are thinking.
(2) You may wish to consider what I found in a Google e-book
(from the year 1908) entitled The Inland Printer: Volume 40:
Nine times out of ten, "two-thirds" does not mean two individual
thirds but one quantity equal to two third portions put together.
(That is why the book tells printers to use a hyphen between
"two" and "thirds.")
(3) I am a learner like you, so I understand that you want a rule to
give you confidence. In such a sentence such as yours, you would
probably always be "correct" if you used the singular.
P.S. If a of- phrase follows "two-thirds," however, that is a different
matter. Study the excellent examples given us by Teacher Soup.
I'm struggling to make two thirds equal 33.33.