になる to express "coming"


During a Japanese lesson, we saw quickly that example:

> Q: 今晩の晩ご飯は何人になりますか。  
>  R: 私を入れて5人です。

Can someone explain to me the meaning of "になります" in this example? Is it a
specific use (against the typical meaning of state change)?




Sorry but it's gramatically incorrect in Japanese (many of Japanese people use
it though). なります here doesn't have specific meaning. 今晩の晩ご飯は何人になりますか。means
"how many people are coming to tonight's dinner?". Verb なる itself has meaning
of become. But somehow we misuse it when we normally use it at polite. Common
mistake is 千円になります instead of 千円でございます (this product costs ¥1000) when shop
staff tells customer the price of product. 千円になります literally sounds something
becomes ¥1000.

