If you take out “an astonishing number of”, the sentence should still be gramatically correct, therefore it should be ARE. Conclusions is plural, so it’s ARE.

“an astonishing number of” acts as an adjective in this sentence. It may be clearer if you replace that phrase with any adjective:

Ex. There are many conclusions…

Ex. There are several conclusions…

The subject is conclusions and the verb is the verb to be. Since the subject is 3rd person plural, the verb will be “are”. Hope this is helpful!

————————————————————————————

So I checked back in on this question, and am amazed that there is still a debate. A simple solution? Type the sentence into Word and check grammar. It will replace “is” with ARE!!!

There ARE an astonishing number….sounds better to me.

Yes- “are” is the correct choice. It wouldn’t make sense to say “There is a number of conclusions.” See what I mean?

you use ‘are’ if you are describing multiple objects…eg “the pencils are yellow”

you also use ‘is’ and ‘are’ when conjugating the verb ‘to be’:

first person is “i am tall”

second person is “you are tall”

and third person is “he/she is tall”

you also use ‘are’ in the plural:

first person plural “we are tall”

second person plural “you are tall”

third person plural “they are tall”

hope that helps

(ps the answer to your homework is ‘is’ because there is only 1 astonishing number, not multiple astonishing numbers)

As it’s linked to the plural form of conclusions.