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Calendar Problem | TOMATO objective 13

Try this beautiful problem from TOMATO Objective no. 13 based on Calendar Problem. This problem is useful for BSc Maths and Stats Entrance Exams.


June 10, 1979, was a SUNDAY. Then May 10, 1972, was a

(A) Wednesday;

(B) Friday;

(C) Sunday;

(D) Tuesday;


In a (non-leap) year there are 365 days.

365 \equiv 1 \mod 7

On a leap year, there are 366 days

366 \equiv 2 \mod 7

From 1972 to 1979, there are 7 years (1 of them is leap year). For each non-leap year, we have to go back 1 day and for every leap year, we have to go back 2 days. Hence in total, we have to go back 8 days for those 7 years. Also, May has 31 days. Hence we have to go back 31+8 = 39 days.

Thus 39 \equiv 4 \mod 7 days before Sunday is a Wednesday.

Answer: (A) Wednesday.

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