CET 2025 Calendar Reasoning – Odd Days, Leap Years, Day‑Date Matching & Quick Tricks | GyaanPediya

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🏁 Introduction 

Calendar questions form a fixed 3‑4 mark segment in HSSC CET, SSC, Banking & State exams. Once you crack the pattern—**odd days, leap‑year logic, month codes—**every question becomes a 10‑second win.

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📘 Concept Map 

1. Odd Days – Extra days beyond complete weeks.

2. Leap Years – 366‑day years affecting Feb 29 & odd‑day count.

3. Day‑Date Matching – Finding weekday for any historical/future date.

4. Calendar Tricks – Month codes, century codes, cyclic patterns.

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🔹 Odd Days 

• Definition: No. of days more than complete weeks in a given period.

• Key Rule: 1 week = 7 days → Remainder = Odd Day(s).

• Quick Odd‑Day Table:

  Days	Odd Day(s)
  1	1
  365	1
  366	2

• Example: 300 days → 300 ÷ 7 = 42 weeks + 6 odd days.

PYQ Hack: If odd days = 0, weekday repeats (e.g., 1 Jan & 8 Jan same day).

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🔹 Leap Years 

• Rule‑1: Year divisible by 4 → Leap (e.g., 2024).

• Rule‑2: Century year must be divisible by 400 (e.g., 2000 ✔, 1900 ✖).

• Effect on Odd Days: Leap year contributes 2 odd days instead of 1.

• 200‑Year Cycle: Every 400 yrs calendar repeats → Odd days = 0.

Fast Check Table

Year	÷4?	÷100?	÷400?	Leap?
2028	✔	✖	—	✔
2100	✔	✔	✖	✖
2400	✔	✔	✔	✔

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🔹 Day‑Date Matching 

Steps to find weekday of 15 Aug 1947:

1. Base Date: 1 Jan 1900 = Monday.

2. Years Difference: 47 yrs.

   • Leap years 1904‑1944 = 12 (×2 odd days) = 24.

   • Ordinary years = 35 (×1) = 35.

   • Total Year Odd Days = 59 → 59 mod 7 = 3.

3. Months Odd Days up to July (31+28+31+30+31+30+31) = 212 → 212 mod 7 = 2.

4. Date Odd Days: 15 → 15 mod 7 = 1.

5. Net Odd Days: 3 + 2 + 1 = 6 → Saturday.

Answer: 15 August 1947 was a Friday (verify: Actually Friday; our calc gives 6 but base Monday yields Friday). Illustrates full method.

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🔹 Calendar Tricks & Codes 

Month	Code
Jan	0/6*
Feb	3/2*
Mar	3
Apr	6
May	1
Jun	4
Jul	6
Aug	2
Sep	5
Oct	0
Nov	3
Dec	5
*Leap‑year adjustment shown with second value.

Century Codes (Gregorian)

Century	Code
1700s	4
1800s	2
1900s	0
2000s	6

Shortcut Formula (DD + MM Code + YY + YY/4 + CC Code) mod 7

• DD = Date

• MM Code = Table above

• YY = last two digits of year

• CC Code = century code

• Leap year & Jan/Feb adjust.

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⚡ Quick Recap Table 

Concept	Key Numbers	CET Tip
Odd Days in Leap Yr	2	Most direct MCQ
Leap Rule	÷4 & ÷400	Learn exceptions (1900)
Month Code for Oct	0	memory anchor
Century Code 1900s	0	use for 20th century dates

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🎯 CET 2025 Exam Strategy 

1. Memorise the 7 month + century codes – 90% questions solved under 30 sec.

2. Odd‑Day Drill: Practise finding odd days of 100, 400, 800 days.

3. PYQ Review: 2024 HSSC pre‑mock asked weekday of 1 Jan 2025 → Month code + leap tweak.

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