Yes Ashley , If you notice I stated previously " A great number of houses" without "The" . I didn't notice "The". Your teacher is right. In this case you can ONLY use " a great many". "The" in "the houses" makes the number of houses definite . " ------ of the houses".what comes before it has to be indefinite or partial ,like part of this definite number so you can only use " a great many"in this example ( in other examples "some" could also be used,if the indefinite number of houses is small). "A great number" is already a definite number .You can't say " a great number of the houses" .

Hello Ashley , You could use both ,they would give a different meaning though: A great number of houses means a large definite number . A great many of houses means a large indefinite number . So it depends on the context ,although I think it would be rather " a great many " in this context,since it is difficult to identify the number of knocked down buildings.

Hey Ashley. Both seem okay to me, though "a great number of the houses" sounds a bit more archaic while "a great many of the houses" sounds stilted and I would say "Many of the" or "Most of the". However, the most important here is that your teacher believes that one or the other is "correct". If your teacher is open-minded, then you can use "Google" to find both examples ("a great many" turns up around 2000 hits while "a great number" only about 75) and demonstrate that perhaps it does not depend on the "the" in the sentence as much as on the context of the sentence or the original source of the sentence. If your teacher is very strict about "right" and "wrong" answers, though, then it is best to not say anything and accept and learn what he/she thinks is correct until you have changed teachers. peace, Mr Spears