Question

Some poeple believe that Jan 1,2000is the first day of the 21st century.Other poeple beleive that the honor belongs to the Jan 1,2001.But everyone should agree that Jan 1,2002 is the first"sum-day" of the new century when you write out that date in standard notation,it becomes 01/01/02,and 1+1=2 .More generally,a sum-day is a date in which the day and month add up to the year. With that in mind:What is the last sum-day of the 21st century ?.How many sum-days are there in the 21st century?

Answer 1

The last sum day will be 12/31/43

In 2011 itself, we have:
01/10
02/09
03/08
04/07
05/06
06/05
07/04
08/03
09/02
10/01