Calendar Basics
Odd Days:
We are supposed to find the day of the week on a given date. For this, we use the concept of ‘odd days’.
In a given period, the number of days more than the complete weeks are called odd days.
Leap Year:
(i). Every year divisible by 4 is a leap year, if it is not a century.
(ii). Every 4th century (divisible by 400) is a leap year and no other century is a leap year.
Note: A leap year has 366 days.
Examples:
Each of the years 1948, 2004, 2008, 2012 etc. is a leap year.
Each of the years 400, 800, 1200, 1600, 2000 etc. is a leap year.
None of the years 1947, 1950, 2013, 2014, 2015, 2100, 1900 etc. is not a leap year.
Counting of Odd Days:
1 ordinary year = 365 days = (52 weeks + 1 day). 1 ordinary year has 1 odd day.
1 leap year = 366 days = (52 weeks + 2 days). 1 leap year has 2 odd days.
100 years = 76 ordinary years + 24 leap years = (76 x 1 + 24 x 2) odd days = 124 odd days.
= (17 weeks + days) 5 odd days.
Number of odd days in 100 years = 5.
Number of odd days in 200 years = (5 x 2) 3 odd days.
Number of odd days in 300 years = (5 x 3) 1 odd day.
Number of odd days in 400 years = (5 x 4 + 1) 0 odd day.
Similarly, each one of 800 years, 1200 years, 1600 years, 2000 years etc. has 0 odd days.
Day of the Week Related to Odd Days:
| No. of days: | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
| Day: | Sun. | Mon. | Tues. | Wed. | Thurs. | Fri. | Sat. |
