I. Not necessarily. All may be born in Tuesday, for example.
II. Yes, for there are only 7 days in a week.
III. Yes, for there are 12 months for a given year.
Mathematically, this is called "the Pigeonhole Principle".
Former Senior Instructor, Manhattan GMAT and VeritasPrep
Vice President, Midtown NYC Investment Bank, Structured Finance IT
MFE, Haas School of Business, UC Berkeley, Class of 2005
MBA, Anderson School of Management, UCLA, Class of 1993