Dear all,


Someone told me that this sentence is correct but I would be grateful if you could confirm it by return email:



Fractions was one idea which Al-Nasawi explained in "Al-Mughni Fil Hissab Al-Hindi".



As you note, "fractions" is a plural word, whereas the verb "was" is singular.



He said that "fractions" refers to the "concept/idea of fractions", so the subject, while it looks like a plural word, is actually singular.



Yours faithfully,

AG

"Fractions was" is fine. This happens quite often. Here's another example:

Cows in a field is something you don't see where I live.

Cows....is....

It's okay because it's a singular concept. This example is better aligned to yours:

Jaws is a great film.





Here's more on subject-verb agreement.