Here is an interesting way to find the day of your birth! No paper, no pen nor cumbersome calculations!

Let us take as an example, a date in the 20th century, 15th August 1947.

Take the last two digits of the year i.e. 47; divide it by 4 and add the quotient to the number 47+11=58; divide this number by 7 (a week has 7 days!) and get the remainder i.e. 2.This is the key number for the year 1947.

Memorize the words "GULF  SMOKE  GUN". The letters of the words represent the twelve months in order.

In our example date, the month is August, the eighth month of the year. The eighth letter in the clue words is 'K'. 'K' is the 11th letter of the alphabet (count with your fingers!); add the digits 1+1 =2. So the key number for the month August is 2.

Now add the key numbers of the year, month and the date (15). 2+2+15 =19. Dividing 19 by 7 we get the remainder as 5.                    

Monday = 1, Tuesday = 2, Wednesday = 3 Thursday = 4 Friday = 5 Saturday = 6, Sunday = 7 or 0.

Hence 15/8/1947 was a Friday!

Note: If it is a Leap year, the key numbers for January and February will be one less i.e. January = 6 and February = 2

Let us find  the day on 12-2-1992.

92 divided by 4 gives the quotient as 23; adding 92and 23, we get 115; dividing the number by 7 the remainder is 3. So the key number for the year is 3.

February is the second month of the English calendar. The 2nd letter in the clue words is 'U'; it is the 21st  letter of the alphabet. 2 + 1 = 3. But as 1992 was a Leap year, 3 -1 = 2. So the key number for the month February is 2.

Adding the key numbers of the year and the month, and the date we get 3 + 2 + 12 = 17. Dividing 17 by 7, the remainder is 3. The third day of the week starting from Monday is Wednesday. So 12th February 1992 was a Wednesday!

The above method can be applied to the 21st century too! But you will have to count the days  from Sunday!

What is the day on 31-10-2002?

02 isn't divisible by 4; dividing by 7 the remainder is 2 itself. Hence the key number of the year 2002 is 2.

The 10th letter of the clue words is 'G', which is the 7th letter of the alphabet. So the key number for  October is 7 or 0.

Adding the key numbers of the year and the month, and the date, we get 2 + 0 + 31 = 33 = 5 (dividing by 7). Counting from Sunday, it is Thursday! 31-10-2002 was a Thursday!

It is interesting, isn't it?

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Just refreshing the thread.

I got lost after the first sentence, looks good but I could never remember those formulae.