Thursday, November 5, 2009


For solving the calendar problems we may need the following info.

  • We can find the number day on which a particular date falls by finding the number of odd days.

  • Odd days are obtained by finding the remainder when the no of days are divided by 7

  • The no of days in each month in a year is Jan-31, Feb-28(29), Mar-31, Apr-30, May-31, Jun-30, Jul-31, Aug-31, Sep-30, Oct-31, Nov-30, Dec-31

  • No of odd days in each month in a year -Jan-3, Feb-0(1), Mar-3, Apr-2, May-3, Jun-2, Jul-3, Aug-3, Sep-2, Oct-3, Nov-2, Dec-3

  • Leap year: A year is said to be Leap year if it contains366 days (ie,29 days in February)
    How to find whether a year is leap year or not ?
    1) We get a leap year if that year is divisible by 4 exactly
    2) Years divisible by 100 and not by 400 is not a leap year

  • 1st January 0001 was a Monday.

  • Calendar repeats after every 400 years.

  • Calendar moves ahead by number of odd days.

  • In a normal year 1st January and 2nd July and 1st October fall on the same day.

  • In a leap year 1st January 1st July and 30th September fall on the same day.

  • Ordinary year = 52 weeks + 1 odd day

  • Leap year = 52 weeks + 2 odd day

  • 100 Years = 76 ordinary years +24 leap years
    100 years has 5 odd days
    400 years has (20+1) odd days ie , 0 odd days.

  • Here are the steps to find out the number of odd days.
    Step 1: Find leap year or not.
    Step 2: Find out total odd days on months.
    Step 3: Find out the total odd days on year.
    Step 4: Finally add the total number of odd days between the given dates.

  • Jan 1, 2001 is a Monday, depending on odd day, we have
    1 is Monday
    2 is Tuesday
    3 is Wednesday
    4 is Thursday
    5 is Friday
    6 is Saturday
    0 or 7 is Sunday