two thirds (equal / equals) thirty-three point thirty-three.
Thank you.
***** 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.