NOT A TEACHER
(1) You are correct: this is a very confusing matter.
(2) First, I think the following are correct:
(a) The number of people waiting in line is 100.
(b) A number of people are waiting in line. (A number of = many)
(3) When a sentence starts with "there," my teachers told me to forget that
word when analyzing the sentence. So we have:
Are a large supply of pens and notebooks in the storeroom.
(4) Now we need to put the words in "regular" order:
A large supply of pens and notebooks ___ in the storeroom.
(a) Do we put "is" or "are" in the space?
(i) Well, let's delete (erase) the "unnecessary" words "of pens and notebooks."
(b) We now have:
A large supply ____ in the storeroom.
Which word sounds better to you: "is" or "are"?
Student or Learner