A Cool Math Trick!

Suppose you’re trying to schedule an upcoming event and you need to know the day of the week that this event will occur on. Can you do that in your head?

Sure you can! You just need to know this little trick! (Brought to us by Stephen C. Tan.)

I found this while looking through some articles at ezinearticles.com

Ultimate Mental Math Trick

Can you tell the day for any date without a calendar at hand? Is that really possible?

It is actually a simple skill that any one can learn. It is also very practical as you may always consider your availability for an activity or an event or you just need to know the day of anyone’s birthday. All you need is a little bit of practice, then you can quickly and easily tell the day of the week of practically any date in history or in the future.

Here’s the Secret

You may need to memorize some codes to learn this trick, but they are very easy to remember.

First, we assign a code number to every day of the week.

Monday – 1

Tuesday – 2

Wednesday – 3

Thursday – 4

Friday – 5

Saturday – 6

Sunday – 7 or 0

Second, we assign a code number for every month of the year. These month codes are used for every year with two exceptions. In a leap year, the month code for January is 5 and for February is 1. The month codes with the corresponding mnemonics are as follows:

January – 6 (WINTER has 6 letters)

February – 2 (2nd month)

March – 2 (You march with 2 feet)

April – 5 (APRIL has 5 letters)

May – 0 (MAY0 for mayonnaise)

June – 3 (JUN has 3 letters)

July – 5 (JULIE has 5 letters)

August – 1 (August begins with an A, the 1st letter)

September – 4 (SEPT has 4 letters)

October – 6 (Halloween TRICKS or TREATS have 6 letters each)

November – 2 (2nd last month)

December – 4 (XMAS has 4 letters)

Third, we assign a code number for every year. For example, the year code for 2011 is 6.

The Formula

Day of the week = (Month code + Date + Year Code) mod 7

Note: mod 7 indicates the remainder you get when you divide by 7.


What is the day for July 16, 2011?

Day of the week = (Month code + Date + Year Code) mod 7

Day of the week = (5 + 16 + 6) mod 7 = 27 mod 7 = 6 (Therefore, it’s a Saturday)

What is the day for December 25, 2011?

Day of the week = (Month code + Date + Year Code) mod 7

Day of the week = (4 + 25 + 6) mod 7 = 35 mod 7 = 0 (Therefore, it’s a Sunday)

Hooray! With constant practice, you are now ready to be the walking calendar. Amaze your friends, colleagues, students, teachers and everyone else.

For further information on how to find the year code of any year, check out my blog at www.themathblog.com

You’ll need to visit Stephen’s blog to get the code for other years, but it’s a very cool trick! Don’t you agree?

Technorati Tags: , , , , , , , , , , , , , , , , , , ,