Logic Puzzle

Two days ago Michael was nine years old. Next year he will be 12 years old. What day of the year is his birthday?


Answer: December 31

The base date is January 1 2010. Two days ago(December 30 2009), Michael's age is 9

January 1 2010 = 10
December 31 2009 = 10
December 30 2009 = 9

Michael's age of December 31 2010 is 11
Next year, 2011 (December 31 2011), Michael's age is 12



Source: http://wiki.answers.com/Q/Two_days_ago_Michael_was_nine_years_old._Next_year_he_will_be_12_years_old._What_day_of_the_year_is_his_birthday