Thank you very much for responding, but I must respectfully disagree. I think it falls under the category of "Idiomatic expressions that designate quantities or parts."
MGMAT SC guide p. 41 states "Idiomatic expressions that designate quantities or parts, such as
a number of, the subject of the sentence is in an Of-prepositional phrase. These expressions provide the exception to the rule that the subject cannot be in a prepositional phrase."
Both of the following are correct:
One-third of the city is unemployed.
One-third of the people are unemployed.
And most importantly from a retired official test:
In an effort improve the quality of patient care, Dr. Lydia Temoscho is directing one of several clinical research projects that
seek to determine the extent that psychological counseling helps to supplement the medical treatment of serious disease.
(A) seek to determine the extent that psychological counseling helps to supplement
(B) seek to determine how helpful psychological counseling is in supplementing
(C) seeks to determine how helpful psychological counseling is to supplement
(D) seeks to determine to what extent psychological counseling is a help in supplementing
(E) seeks to determine the extent that psychological counseling is helpful in supplementing
OA=B
Please let me know if you disagree.
That's right. You should be focusing on the keyword: WHO - which implies further description of the second half of the phrase TEACHERS.
Teachers is plural so you use WERE.
Here PROJECTS is further described - and since PROJECTS is plural, you use SEEK.