Can you find out what day of the week was January 12, 1979?

Solution: 3

As 12th January, 1979 = 1900 years + 78 years + period from 1st Jan. to 12 Jan. 1979

So No. of odd days in 1600 years = 0

No. of odd days in 300 years (1900 – 1600) = (5 × 3) ÷ 7 = 2 weeks + 1 odd day

No. of odd days in 78 years = 19 leap year + 59 ordinary years

= {(19 × 2) + (59 × 1)} ÷ 7= (38 + 59) ÷ 7 = 97 ÷ 7 =13 weeks + 6 odd days

No. of odd days in period from 1st Jan. to 12 Jan. 1979 = 12 days = 12 ÷ 7 = 1 week + 5 odd days

Total odd days = 1 + 6 + 5 = 12 days = 12 ÷ 7 = 1 week + 5 odd days

So 12th January, 1979 is Friday as Sunday is 0; Monday is 1 and so on.

Note:

1) A leap year is a year which is divisible by 4.

2) No. of odd days in a leap year is 2 and in an ordinary year is 1

3) No. of odd days in each 100 years is 5 and each multiple of 400 is 0.