about 廿 and 卅
Hi, how much are they used?
Do I always have to use 廿 in the place of 二十么?

And how do I read 廿五? -- èrwŭ or niànwŭ ??

Question

about 廿 and 卅
Hi, how much are they used? 
Do I always have to use 廿 in the place of 二十么?

And how do I read 廿五? -- èrwŭ or niànwŭ ??

Answer

二十四史  e' famosa che e' un serie di history

Answer

廿 is pronounced nian4. It is used in really formal situations sometimes, but is not commonly used. I have written it in essays before and my teachers have never said anything about it. 
卅 (and 卌) are only really used in Cantonese/some classical Chinese texts I believe.

Answer

廿四史
[ niàn sì shǐ ] 
基本释义
[ niàn sì shǐ ]
即二十四史。《二十年目睹之怪现状》第二二回:“伯述 叹道:‘现在的世界，不能死守着 中国 的古籍做榜样的了！你不过看了《廿四史》上，五胡大闹时，他们到了 中国，都变成 中国 样子，归了 中国 教化。’”详“二十四史”。

Answer

They're rarely used几乎不用
It pronounces as niàn

Answer

生活中一般不用这个字，常见的就是在阴历日期中，一般就读作二十