# Calendars

### Calendar Important Formula’s

• 1 ordinary year = 365 days = (52 weeks + 1 day.)
• 1 ordinary year has 1 odd day. 1 leap year has 2 odd days. = (76 x 1 + 24 x 2) odd days = 124 odd days.

### Remember the Number of days in a Months for calendar.

1. April
2. June
3. September
4. November

1. January
2. March
3. May
4. July
5. August
6. October
7. December

#### Special Month : February

• Depending on whether the year is a leap year or not.
• Leap years are exactly divisible by 4
• February can have : 28 Days  or 29 Days (For Leap Year)

### Formulas Summary for Calendars:

•  A leap year has 366 days
• Every year divisible by 4 is a leap year, if it is not a century.
• Every 4th century is a leap year and no other century is a leap year.
• Counting odd days
1 ordinary year ≡ 365 days ≡ (52 weeks + 1 day)
Hence number of odd days in 1 ordinary year= 1.
1 leap year = 366 days = (52 weeks + 2 days)
Hence number of odd days in 1 leap year= 2.
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.
Hence number of odd days in 100 years = 5.
Number of odd days in 200 years = (5 x 2) = 10 = 3 odd days