Date Writing In Formal Language

[AtlasAkin]

We are having a conference, a formal conference. I would like to ask what is the formal writing of 2011? Is 11' a formal writing style? Should we just write 11 or 2011?

 

[bhaisahab]

We are having a conference, a formal conference. I would like to ask what is the formal writing of 2011? Is 11' a formal writing style? Should we just write 11 or 2011?

I would write "2011".