This is pretty much the most awesome skill ever. I don’t even know why I tell it to you. With this skill girls will beg you to be their boyfriend (also boys will beg girls to be their girlfriend). Use this skill with care. I don’t take any responsebility for the awesomeness that will occur in your life.

Example: You will learn which day of the week 2.january 1986 was (it was a thursday)

Here it goes:

The first thing you need is to that each day of the week is assigned a unique number.

Monday: 1, Tuesday:2, Wedensday: 3, Thursday: 4, Friday:5, Saturday:6, Sunday:7/0.

Every month is assigned a unique number:

January: 6 (5 in leap year) (Rule to remember: W-I-N-T-E-R has six letters)
February: 2 (1 in leap year) (Rule to remember: 2nd month of the year)
March: 2 (Rule to remember: 2nd beat of the drum)
April: 5 (Rule to remember: A-P-R-I-L has five letters)
May: 0 (Rule to remember: May-0)
June: 3 (Rule to remember: June B-U-G has three letters)
July: 5 (Rule to remember: Watching FIVER-works)
August:1 (Rule to remember: Begins with A, 1st letter)
Sept: 4 (Rule to remember: Start of F-A-L-L)
Oct: 6 (Rule to remember: Halloween T-R-I-C-K-S)
Nov: 2 (Rule to remember: 2 servings of TUrkey please!)
Dec: 4 (Rule to remember: L-A-S-T month

Remembering these months is the hardest part of the trick, but it actually just takes 2 min to learn. Now to the easy part.
Every year has a yearcode. 2006 yearcode is 0. To calculate the day of the week for dec 3, 2006:
Month code + Date +Yearcode = 4 + 3 + 0 = 7. Hence this date will be on day 7, which is Sunday.

What about Nov 18, 2006? Nov has a month code of 2 we have: 2 + 18 + 0 = 20. We then subract any multiple of 7 from our answer. We then get 6. Hence Nov 18 2006 occurs on Saturday.

Not all yearcodes are zero. But they are easy to calculate. Days after year 2000:
2000 + x years. We take the number x/4 (ignoring any remainder) and add that to x. The year code can be reduced by subracting any multiple of 7.
Example: With 2061, we that 61/4 = 15 (with a remainder of 1 that we ignore). Thus 2061 has a year code of 61+15 = 76. We subract any multiple of 7. 76-70 = 6

Hence March 19, 2061 has: 2 + 19 + 6 + = 27. 27 - 21 = 6. Which is a saturday.

For dates between 1900-1999 you do exactly the same. Just that you add one to your yearcode.
It might be helpful to learn the multiples of 7 to calculate faster: 7,14,21,28,35,42,49,56,63,70,77,84,91,98,105,112,119,126.

This was grabbed from a cool book by Arthur Benjamin called Secrets of Mental Math

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