## Archive for December 21, 2012

### Is It Yours? It’s Not Mayan…

It’s December 21. You’re here. I’m here. So much for the prophecy of the Mayan calendar.

So, will someone please call Ms. Angelou and tell her she had it wrong?

Actually, the Mayan calendar never predicted the apocalypse. (Nor was it developed by Maya Angelou. Or Maya Rudolph. or Maya Lin. Or anyone else named Maya.) In truth, one cycle of the Mayan calendar is ending, so a new cycle is about to begin. It’s not a like a time bomb that will explode when the cycle ends. It’s more like the odometer of a car rolling over.

While I can forgive folks who misread the Mayan calendar, I have less patience for folks who misunderstand *our* calendar.

I recently received an email that stated the following:

This year, December has five Saturdays, five Sundays, and five Mondays. This will only happen once every 824 years.

Oish. Really? I wish that folks who forward this kind of nonsense would, at a minimum, look at a calendar. (At a maximum, I wish they would lose my contact info.)

The good folks at www.timeanddate.com will gladly show you the calendar for December of any year you like. And if you look at the calendar for December in 2018, 2029, 2035, 2040, 2046, 2057, 2063, 2068, 2074, 2085, 2091, 2096, or any of 105 other years within 824 years of today, you’ll see that they all have five Saturdays, five Sundays, and five Mondays. Consequently, it doesn’t seem that December 2012 is terribly special.

The folks at www.timeanddate.com also have a nice explanation of why the math in the email that I received is all wrong (though their article is based on July 2011 which had five Fridays, five Saturdays and five Sundays, and they disprove an argument saying that such an occurrence happens once every 823 years; but, whatever).

I suspect that most folks are unaware that our calendar repeats in a 28‑year cycle. And I’d bet that even fewer realize there is a nice pattern of 6‑11‑6‑5 years when the calendar repeats… assuming you skip those nasty century years, like 1900 and 2100, that fail to include a leap day.

Still, I think most reasonably intelligent humans should recognize that a claim like “only once every 824 years” has to be an exaggeration.

But perhaps that’s the problem: I’m assuming that people who forward emails like this are reasonably intelligent.

Along similar lines, here’s a math trick that I’ve received several times via email:

- Take the last two digits of the year in which you were born.
- Now add the age you will be this year. (That is, if you’ve already had your birthday this year, add your current age. If you haven’t, add the age you’ll turn on your birthday this year.)
- The result will be 112 for
*everyone in the whole, wide world*.

There’s only one problem with this trick: It doesn’t work.

For someone like Besse Cooper, who was born in 1896, the result will be 212.

For someone like my twin five-year-old sons, who were born in 2007, the result will be 12.

In fact, the trick won’t work for anyone born before 1900 or after 2000. Based on data about age distribution, the result will not be 112 for approximately 15% of the U.S. population. The yellow bars in the graph below indicate the ages for which this trick does not work.

A better statement of this “trick” might be…

- Take the year in which you were born.
- Now add the age that you will be this year.
- The result will be 2012 for everyone in the whole, wide world.

Completely correct! But not much of a trick anymore, is it?

### The Twelve Days of Crisp Math – Day 10

It’s the **Tenth Day of Crisp Math**, and there are lots of jokes involving the number 10.

How many tents can a campground hold?

Ten, because ten tents make a whole.

The following is for those students who didn’t do much during the fall semester, but who think they can engender some good will by giving a holiday gift to their professors.

A failing student showed up to the math professor’s office with a hundred-dollar bottle of scotch. The professor objected, “I’m sorry, taking a gift from a student would be unethical.”

The student said, “I understand. But what if I sell it to you for $10?”

The math professor thought for a moment. “At that price, I’ll take a whole case!”