While I was in grad school, I helped to make ends meet by tutoring high school students. Believe or not, I’m actually high-school competent in a wide variety of subjects. Unfortunately, though, a lot high school-level work follows this pattern: plug numbers into formula, write answer, move on. While this might not sound like a bad strategy, my students often accepted that whatever answer they got must be correct, by virtue of having been spit out by their calculators.^*

Conversations tended to go like this.

Me (watching student scribble down answer to physics problem): “Do you really think that 147 divided by 40 is 36.75?”
Student: “Oh. No. That doesn’t make sense.”
Me: “If it doesn’t look right, it probably isn’t right. Let’s try that again.”^**

I had the same reaction this afternoon when I read an interesting tidbit in the Passport blog on the coming New Year in Ethiopia, which is going to be celebrating the new millennium, only seven years and eight months after the rest of us.
Prerna Mankad writes:

Following the Julian calendar, which is seven years and eight months behind the Gregorian calendar, Ethiopia will welcome the first day of the third millennium on September 12.

Very interesting, except that the difference between the Julian and Gregorian calendars is a matter of days, not years. For example, as far as the rest of the world is concerned, the great October Revolution actually occurred on November 7, rather than October 24 (“Hunt for Red November” doesn’t quite have the same ring to it, does it?). But both calendars agree that Revolution occurred in 1917.

So, for there to be a difference of almost eight years, there has to be something else going on. Sure enough, according to Wikipedia (don’t shoot me–it’s the easiest source to turn up quick answers, and I have no reason to suspect that Colbert nation has been messing with the calendar entries) the Ethiopian Orthodox Church uses a different calculation for the birth of Christ.

In Mankad’s defense, the article cited in the post makes the same error, asserting that the disparity between millennia is due to Ethiopia’s use of the Julian calendar. Still, knowing when to question received wisdom is an important life skill (one that I’m still working on). Sometimes that gut check is an important one.

^* Tutoring kids is not just about making sure they get the concepts–it’s about making sure that they have the necessary study and test-taking skills to demonstrate that they get it. Stupid errors are a big cost for many of these kids. They understand what they are supposed to do with the formula and why, but they get lousy grades because they make dumb mistakes.
^** A tip for those of you with school-aged kids: textbook math/science problems almost always have a round number or a neat fraction (1/2, 1/3, 1/4, etc.) for their answer. If you do the calculations on a word problem and get 31.4332456, it’s probably a wrong answer, unless you are doing a lesson on rounding. This annoys me, however, since real world math does not tend to produce round numbers.

Update: after I emailed the author, Passport has corrected the post.