Railways Notes / Mathematics (Quantitative Aptitude) / Chapter 28
Chapter 28 of 31

Calendar

The odd days concept — the single technique used to find the day of the week for any given date.

📖 ~4 min read 📐 RRB NTPC / Group D — Mathematics

Odd Days Concept

  • Odd days = number of days beyond complete weeks in a given period
  • 1 ordinary year (365 days) = 52 weeks + 1 odd day
  • 1 leap year (366 days) = 52 weeks + 2 odd days

Century Odd Days

PeriodOdd Days
100 years5
200 years3
300 years1
400 years0

Day Reference Table (Odd Days → Day)

Odd DaysDay
0Sunday
1Monday
2Tuesday
3Wednesday
4Thursday
5Friday
6Saturday

Leap Year Rule

A year is a leap year if divisible by 4, EXCEPT century years (ending in 00) which must be divisible by 400 (e.g., 2000 is a leap year, 1900 is not).

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