Calendar
A calendar is chart or series of pages showing the days, weeks and months of a particular year. A calendar consist of 365 or 366 days divided into 12 months.
Important Points Related to Calendar
1. Ordinary Year:
The year which is not a leap year is called an ordinary years. An ordinary year has 365 days.
(52 complete weeks + 1 extra day = 365 days)
2. Leap Year:
A leap year has 366 days (the extra day is 29th of February) (52 complete weeks + 2 extra days = 366 days.)
(i). A leap year is divisible by 4 except for a century. For a century to be a leap year it must be divisible by 400.
(ii). Every 4th century is a leap year and no other century is a leap year.
Note: A leap year has 366 days.
Examples:
i. Years like 1988, 2008, 1676 are leap year (divisible by 4).
ii. Centuries like 2000, 2400 are leap year (divisible by 400).
iii. None of the years 2001, 2002, 2003, 2005, 2017 is a leap year (not divisible by 4).
iv. Centuries like 1700, 1800 are not leap year (not divisible by 400).
v. In a century, there is 76 ordinary year and 24 leap years.
3. Odd Days:
Extra days, apart from the complete weeks in a given period are called odd days. An ordinary year has 1 odd day while a leap year has 2 odd days.
To find the numbers of odd days
1. 1 ordinary year = 365 days = (52 x 7) + 1 = 52 weeks + 1 odd day.
1 ordinary year has 1 odd day.
2. Number of days in a leap year = 366 days = (52 weeks + 2 days)
A leap year has 2 odd days.
3. Number of days in a century (100 years)
= 76 ordinary years + 24 leap years
= (76 x 1 + 24 x 2) odd days = 124 odd days.
= (17 weeks + 5 days) 5 odd days.
Number of odd days in 100 years = 5.
MIND IT !
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.
4. 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. |
5. Day Gain/Loss
Ordinary Year (+/- 1 day)
i. When we proceed forward by 1 yr, then 1 day is gained.
For example: 9th August 2013 is Friday, then 9th August 2014 has to be Friday + 1 = Saturday.
ii. When we move backward by 1 yr, then 1 day is lost.
For example: 24th December 2013 is Tuesday, then 24th December 2012 has to be Tuesday - 1 = Monday
Leap Year (+/- 2 days)
i. When we proceed forward by 1 leap year, then 2 days are gained.
For example: If it is Wednesday on 25th December 2011, then it would be Friday on 25th December 2012 [Wednesday + 2] because 2012 is a leap year.
ii. When we move backward by 1 leap year, then 2 days are lost.
For example: If it is Wednesday on 18th December 2012, then it would be Monday on 18th December 20111. [Wednesday - 2] because 2012 is a leap year.
Exception
The day must have crossed 29th February for adding 2 days otherwise 1 day.
For example: If 26th January 2011 is Wednesday, 26th January 2012 would be Wednesday + 1 = Thursday (even if 2012 is a leap year, we have added + 1 day because 29 February is not crossed).
If 23rd March 20111 is Wednesday, then 23rd March 2012 would be Wednesday + 2 = Friday (+ 2 days 29th February of leap year is crossed).