It would be grammatically correct to usage "are" if the topics were indeed "two" individually, yet they are not.
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By saying "One and one are 2," that means that each "one" is 2. The tantamount would certainly be, "One is two, and also one is two."
Saying "One and one is two" teams "one and one" to be the topic of the sentence. And "one and also one" is 2. ;)
In your short article, you said "which question is grammatically correct?" You would certainly ask, "Is one and also one two?" Although, that can be confmaking use of without somepoint to sepaprice the "one" and also the "two" at the finish. The desired method would certainly be "Does one plus one equal two?"
Fluent English speakers routinely say it both ways.The ever-famous Google ngrams shows that "one and also one is" is substantially even more renowned, however "one and also one are" is still widespread.
Logically, I think it need to be "one and one are". By the normal rules of grammar, that is a compound subject. We wouldn"t say "Bob and also Charlie is ..."; we say "Bob and also Charlie are ..." Etc.
Snailplane"s deleted answer—I don"t recognize why it"s deleted, it appears a valid answer to me—provides the amazing suggest that we sometimes usage such compounds to refer to a solitary unit, prefer "Peanut butter and jjiyuushikan.orgy is my favorite sandwich." I think the essential tbelow is that the words surrounding the "and" are a name or a title, prefer of course we would say, "Pride and Prejudice IS Sally"s favorite book", not "... are Sally"s favorite book", bereason we"re talking around one book whose title happens to have the word "and" in it. It"s not favor Sally likes a book called Pride and she additionally likes a book called Prejudice. Do "one and also one" in this sentence loss into that category? I do not think so.
Even when the allude of a sentence is to say that two are more points are joined in some means, we still use "are". "Bob and also Mary are a pair." "Smith, Jones, and Brown are a dangerous gang." "The four legs are what organize up the table." Etc.
So if you go by prevalent consumption, either is acceptable, yet "is" is slightly desired. If you go by standard rules of grammar, I think "are" is correct. Obviously others answering on below disagree via me. Which, probably, is why we check out the separation in common intake.
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I think you have to feel cost-free to use whichever you prefer. In day-to-day intake no one is most likely to even alert. If you have a teacher or an editor who insists that one is wrong, I"d simply execute whatever before they ask for fairly than argue around it.