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ISRO EC 2025 Q.81: solution and answer

ISRO 2025 · ECQ.81 · 1 mark · MCQ

What was the day of the week on 28th May, 2006? (1 mark)

  1. (A)

    Thursday

  2. (B)

    Friday

  3. (C)

    Saturday

  4. (D)

    Sunday

See the question in the paper
ISRO EC 2025 question 81Tap to open full size

Answer and solution

ANSWER

28 May 2006 was a Sunday, option (d).

Official answer: DSource: ISRO's final answer key of 15 May 2026

  1. Use the odd-days method: reduce the elapsed days to a remainder modulo 7, then count forward from a reference day.

  2. Reference: 1 January 2001 was a Monday. The years 2001 to 2005 are 5 complete years ending on 31 December 2005.

  3. Among 2001 to 2005 only 2004 is a leap year. An ordinary year gives 1 odd day and a leap year gives 2, so the odd days are .

  4. So 1 January 2006 falls 6 days after Monday, which is a Sunday.

  5. Days from 1 January 2006 to 1 May 2006: January 31, February 28 (2006 is not a leap year), March 31, April 30, giving days. Then 27 more days reach 28 May, so 28 May is days after 1 January.

  6. , so the odd days are and the weekday is the same as that of 1 January 2006.

  7. Therefore 28 May 2006 falls on a Sunday, which is option (d).

KEY IDEA

Count odd days (days modulo 7) from a known reference date: an ordinary year adds 1 odd day, a leap year adds 2, and a whole number of weeks adds 0.

WATCH OUT FOR

Counting 2004 as an ordinary year, or treating 2006 as a leap year when adding February's days, shifts the answer by a day. Also easy to stop at 1 January 2006 and forget to add the days up to 28 May.

From the ISRO EC 2025 paper. Also Q.81 of the ISRO Scientist/Engineer Computer Science 2025 paper. Every question of this paper · The full paper (PDF, ISRO) · All 5 ISRO Numerical questions, with notes

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