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Story hook

"15 August 1947 was a Friday. What day was Republic Day, 26 January 1950?"

The calendar candidate panics: "How could anyone know? Look at a calendar? Count 900-odd days?"

The trained candidate calmly does the odd-day math. From 15 Aug 1947 to 15 Aug 1948 → 366 days (1948 is leap; the period includes 29 Feb 1948) → 2 odd days. From 15 Aug 1948 to 15 Aug 1949 → 365 → 1 odd day. From 15 Aug 1949 to 26 Jan 1950 → 164 days = 23 weeks + 3 days → 3 odd days. Total: 2 + 1 + 3 = 6 odd days. Friday + 6 = Thursday. Republic Day 1950 was indeed a Thursday.

This is the CSAT calendar superpower: any date in any year, in 60 seconds, without a calendar. The clock counterpart works the same way — angles between hour and minute hands reduce to arithmetic.

CSAT puts 1-2 calendar/clock questions per paper. They look intimidating but collapse to a tiny formula bank.

Why this matters for UPSC

For CSAT (Paper II, qualifying 33%):

• 1-2 questions per paper on calendar + clock. Steady weight since 2011.
• High difficulty perception, low actual difficulty — candidates often skip these out of fear, leaving free marks.
• A trained candidate solves a calendar question in 60-90 seconds, a clock question in 45-60 seconds.

The block is small but easy to lock in once the rules are internalised. Two correct calendar/clock questions = 4 marks = 6% of the 66-mark qualifying floor.