Calendar Questions

A century means 100 years => 76 normal years and 24 leap years

We know that, a normal year contain 1 odd day (365/7 = 52 weeks + 1 odd day)

a leap year contain 2 odd days (365/7 = 52 weeks + 2 odd days)

100 years => 76 x 1 + 24 x 2 = 124 odd days = 124/7 = (17 weeks + 5 odd days)

200 years => 2 x 5 = 10 = 1 week + 3 odd days

300 years => 3 x 5 = 15 = 2 weeks + 1 odd day

400 years => 4 x 5 = 20 + 1 odd day (leap year) = 3 weeks + 0 odd days

500 years => 5 x 5 = 25+1 = 26/7 = 3 weeks + 5 odd days 

Again repeats...

18 Feb, 2016 = (2015 years + Period from 1.1.2016 to 18.2.2016)

Odd days in 1600 years = 0

Odd days in 400 years = 0

15 years = (12 ordinary years + 3 leap year) = (12 x 1 + 3 x 2)= 4 odd days

Jan  Feb

(31 + 18 ) = 49 days

49 days = (7 weeks + 0 day)= 0 odd day.

Total number of odd days = (0 + 0 + 4 + 0) = 4 odd day.

Given day is Thursday

19th April, 1986 = (1985 years + Period from 1.1.1986 to 19.4.1986)

Odd days in 1600 years = 0

Odd days in 300 years = 1

85 years has 21 leap years + 64 ordinary years.

Number of odd days in 85 years =( 21 x 2 + 64) = 1 odd day.

Jan. Feb. March April

(31 + 28 + 31 + 19) = 109 days

109 days = 15 weeks + 4 days= 4 odd day.

Total number of odd days = (1 + 0 + 1 + 4) = 6.

Given day is Saturday.

28 May, 2006 = (2005 years + Period from 1.1.2006 to 28.5.2006)

Odd days in 1600 years = 0

Odd days in 400 years = 0

5 years = (4 ordinary years + 1 leap year) = (4 x 1 + 1 x 2) 6 odd days

Jan. Feb. March April May

(31 + 28 + 31 + 30 + 28 ) = 148 days

148 days = (21 weeks + 1 day) 1 odd day.

Total number of odd days = (0 + 0 + 6 + 1) = 7 0 odd day.

Given day is Sunday.

On 31st December, 2005 it was Saturday.

Number of odd days from the year 2006 to the year 2009 = (1 + 1 + 2 + 1) = 5 days.

therfore, on 31st December 2009, it was Thursday.

Thus, on 1st Jan, 2010 it is Friday

25 Jan, 1981 = (1980 years + Period from 1.1.1981 to 25.1.1981)

Odd days in 1600 years = 0

Odd days in 300 years = 1

80 years = (60 ordinary years + 20 leap year) = (60 x 1 + 20 x 2)= 2 odd days

Jan = 25 days = (3 weeks + 4 days) = 4 odd days.

Total number of odd days = (0 + 1 + 2 + 4) = 7= 0 odd day.

Given day is Sunday.