Which date of June 2099 among the following is Sunday?

(a) 4
(b) 5
(c) 6
(d) 7 ✓ UPSC's answer

Why the answer is (d)

• Use Zeller's congruence for the Gregorian date 7 June 2099, with q=7, m=6, K=99, and J=20.

• Compute floor(13(m+1)/5)=18, floor(K/4)=24, floor(J/4)=5, and 5J=100.

• Add the terms: 7 + 18 + 99 + 24 + 5 + 100 = 253.

• Divide 253 by 7: 253 = 7 × 36 + 1, and remainder 1 means Sunday.

• Hence 7 June 2099 is Sunday, so option (d) follows.

Why the other options are wrong

(a) 4: Option (a) is wrong because 4 June 2099 is Thursday.
(b) 5: Option (b) is wrong because 5 June 2099 is Friday.
(c) 6: Option (c) is wrong because 6 June 2099 is Saturday.

Asked in the CSAT Paper II of the UPSC Civil Services Preliminary Examination 2022, held on 5 June 2022. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.