".A large number of invitations have been sent.
A large number of invitations has been sent. (slightly formal)"

a number of means several and is a quantifier that modifies the subject invitations in the above sentences.

My question is:

"A large number of invitations has been sent." In this case, what does slightly formal mean?

Does it mean that it does not follow the strict grammatical rules (SV agreement), therefore not so formal?

Or does it mean something else?

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Comments  (Page 3) 
Ant_222«I wonder, does "a number of people has" disrupt ny reading flow? (If it doesn't, I wouldn't know, would I?)» So, does it or not?
I don't remember any case where where I noticed "a number of" + singular verb, so I thinkit doesn't disrupt my reading flow. But I don't know really. It's not something I can test on purpose. Emotion: wink
Yoong LiatYes, 'handphone' is S.E. Asian English. Therefore, the word is not recognised, so it is not advisable to use that word. I'm aware that the word is found in the Oxford Advanced Learner's Dictionary and it states it is used in S.E. Asia, so it is not recognised in British or American English.

I always use "mobile" myself. My point was, if you find it in a dic, its use is recognised to be so common that sooner or later it will become "correct" ... everywhere but not among the Britons, anyway!
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In one of my English usage books, it is stated that 'handphone' is Singlish (Singapore English). The writer, a professor, says that it should not be used. If the word is mainly used in S.E. Asia, it should be avoided. If it is used in England or America, then it may be accepted one day.

I've referred to all the dictionaries, including those available on the website, and 'warded' does not have the meaning 'hospitalised'. In fact, if you ask English experts, the chances are that they will say it does not mean 'hospitalised'.

However, The New Oxford Dictionary of English defines 'warded' as 'hospitalised'. So 'warded' will one day be accepted as having the same meaning as 'hospitalised'.
Just the opposite of "not so formal"--it means that technically the second phrase
InchoateknowledgeA large number of invitations has been sent.
follows the rule of subject-verb number agreement ("number...has") but it sounds odd to many people, who would think that formal grammar is not reasonable here. Because the plural "invitations" is closer to the verb, it would seem that the verb should be plural. This question arises in many contexts.