When do we use "廿", "卅" and "卌"? I am aware of a related question and I know that 


"廿" means 20.
"卅" means 30.
"卌" means 40.


But I am wondering how to use them correctly. When and how do we use "廿", "卅" and "卌"? For example, are the following sentences gramatically correct?


这里距离机场有卌八千米。
我今年卅岁。
今天是四月廿七日。
As far as I know, in Mainland China:

廿 is only used in written lunar calendar. It is very rarely used in spoken Chinese. However, it may be used in some dialects such as Cantonese.
卅 is not used in spoken Chinese, except for representing the 30th day of a month in naming a few historical events and telegraph (popular in early 1900s but rarely used today).
卌 is nearly extinct and should be considered obsolete.

In conclusion: 二十 (&quot;two tens&quot;), 三十 (&quot;three tens&quot;) and 四十 (&quot;four tens&quot;) are enough.