If 31st May, 2011 were the current date, the answer would be "today".
Other options:
1. If 'letter' means "graphic symbol, written character", then the five characters '31511' written with two spaces, i.e. as 31 5 11, is one way of writing 31st may, 2011 in five 'letters'.
2. If 'letter' means a written, typed or printed communication, you can easily write 31st may 2011 in five different letters, sending them either to five different people, or by sending all those five letters to the same person! Either way, you would have written 31st may 2011 in five letters!
You cannot write it in 5 letters, you can write it in 4. Using roman numerals it would be: IX/V/MMXI, this required 4 letters.
today
A date or Today
You cannot (answered 14 June 2012).
You cannot. At least, not with the calendar that is in international use now. 23 May 2011.
If that was the date were currently, the answer would be "today".
i can write 24 May 2011 in five letters answer is TODAY
ACHDB
A date
You cannot (10 May 2011).
You cannot write it in 5 letters, you can write it in 4. Using roman numerals it would be: IX/V/MMXI, this required 4 letters.
Today
Today
Today
today
If the date were 29th May 2011 you could have said "today."
A date or Today