UPSC Prelims 2020 CSAT Paper II · Q20 of 80 Mental Ability medium

If in a particular year 12th January is a Sunday, then which one of the following is correct?

  1. (a) 15th July is a Sunday if the year is a leap year.
  2. (b) 15th July is a Sunday if the year is not a leap year.
  3. (c) 12th July is a Sunday if the year is a leap year. ✓ UPSC's answer
  4. (d) 12th July is not a Sunday if the year is a leap year.

Why the answer is (c)

• 12 January is Sunday; count the days from 12 January to 12 July.

• In a leap year, the interval is 31 + 29 + 31 + 30 + 31 + 30 = 182 days.

• 182 days is exactly 26 weeks, so 12 July is also Sunday in a leap year.

• In a non-leap year, the interval is 31 + 28 + 31 + 30 + 31 + 30 = 181 days, i.e. 25 weeks + 6 days, so 12 July is Saturday.

• 15 July is 3 days after 12 July, making it Wednesday in a leap year and Tuesday in a non-leap year.

• Therefore option (c) is correct.

Why the other options are wrong

(a) 15th July is a Sunday if the year is a leap year.
15th July is Wednesday in a leap year, not Sunday.
(b) 15th July is a Sunday if the year is not a leap year.
15th July is Tuesday in a non-leap year, not Sunday.
(d) 12th July is not a Sunday if the year is a leap year.
12th July is Sunday in a leap year, so it is not correct to say it is not a Sunday.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2020, held on 4 October 2020. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.

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