### Calendars

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__Calender__

Important Points :

**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 is a leap year and no other century is a leap year.

**Ordinary Year:**The year which is not a leap year is called an ordinary years . An ordinary year has 365 days.

__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 odd days

* 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 (Assuming that 1AD January 1st is a Sunday):

Number of Odd Days | 0 | 1 | 2 | 3 | 4 | 5 | 6 |

Day of the week | Sunday | Monday | Tuesday | Wednesday | Thursday | Friday | Saturday |