Important Formulas: Calendar | Logical Reasoning (LR) and Data Interpretation (DI) - CAT PDF Download

Given below are some of the important formulas which must be kept in mind while attempting questions related to Calendars in the CAT exam.

• Odd Days: If the question is asking to find the day of the week on a given date, the students need to use the concept of odd days. 
  • The number of days more than the completed week are called odd days. 
• Leap Year: Every year which is divisible by 4 is a leap year and every fourth century is a leap year and no other century is a leap year.
  • For instance, Each of the years 1948, 2004, 1676 - each of them is a leap year.
  • 400, 800, 1200, 1600, 2000 - each of them is a leap year.
  • 2001, 2002, 2003, 2005, 1800, 2100 - none among them is a leap year.
• Ordinary year: The year which is not a year is called an ordinary year. An ordinary year has a total of 365 days
• Counting of odd days: 1 year has a total of 52 weeks and 1 day. Hence, 1 ordinary year has 1 odd day
  • 1 leap year has 52 weeks and 2 days. Hence, 1 leap year has 2 odd days.
  • 100 years has 76 ordinary years and 24 leap years
  • = (76 x 1 + 24 x 2) odd days = 124 odd days. = (17 weeks + days) 5 odd days. Hence, the number of odd days in 100 years is five
• The number of odd days in 200 years will be (5 X 2)= 3 odd days
• The number of odd days in 300 years will be (5 X 3)= 1 odd day
• The number of odd days in 400 years will be (5 X 4+1)= 0 odd day