# Rambling Thoughts

## Monthly Archives: June 2010

According to my standards, Google has violated its motto of “don’t be evil”. Here’s why:

Search for “pi” on Google: http://www.google.com/#q=pi. You’ll notice that Google’s calculator has helpfully provided an approximate value of pi. But look more closely, and you’ll see that there’s a minor problem:

Google used an equals sign, suggesting that pi is precisely 3.14159265. However, as we all should know, pi is irrational and never terminates, so Google is actually telling us something that is blatantly false. By doing so, it is corrupting the minds of all people who view that webpage. Even worse, Google’s calculator truncates the values of all numbers without any indication; even the value of $\frac13$ is wrong. We must work to stop this nonsense! Please write to Google and ask them to fix this mathematical falsity.

Click to see a surprising insightful commentary on Google’s evil scheming to rid the world of infinite decimals:

## A Converging Rabbit

I’ve decided to make a page of some fun problems. I’m not sure how successful this will be, but in theory, there will eventually be a nice long list of my favorite problems. Here’s the first one:

A rabbit climbs out at its hole, and walks $1$ mile in a straight line. Then, the rabbit repeatedly turns $\pi/3$ radians and walks half of the distance it just walked,
as pictured below.

How far away from the rabbit’s hole is the point at which the rabbit converges?

This is an ARML-style problem: There are lots of ways of solving this, but some methods are cleaner and faster than others. Click to see some solutions.

## ARML

ARML (American Regions Mathematics League) is an annual math contest that takes place every year at four sites around the country. It’s one of my favorite math contests.

ARML is different from most other math contests because it requires teams to travel to one of four central sites. This means that teams have to travel (some times for very long distances) to participate. Inevitably, this means that participation at ARML is not especially high; only 124 teams of fifteen people (in 2010), or less than one percent of the more than 200000 people who participated in the AMC. Teams that do participate at ARML, however, are much more organized; most teams organize several practices before the contest, while some teams prepare for ARML year-round. The team aspect of the contest (3 out of 4 rounds have a team component, together constituting 50% of the total team score) also makes ARML stand out. Indeed, ARML is primarily a team contest, and the team results every year are watched much more closely than the individual high scorers. As a result, ARML is much more social than most other math contests, giving participants a chance to work closely with their team and to meet people from other teams. This social aspect of ARML is what makes ARML enjoyable.

Mathematically, ARML feels different from most other contests. The ARML style is to have problems that look hard but are made much easier through clever tricks. Often, these problems can be solved without being clever, but cleverness can often yield very simple solutions. As an example, consider this year’s coffee mug problem: [EDIT (17 September 2010): Updated with the original wording.]

Let $P(x) = x^2 + 2010 x + 2010$, and let $r$ and $s$ be the roots of $P$. If $Q$ is a quadratic polynomial with leading coefficient 1 and roots $r + 1$ and $s + 1$, compute the sum of the coefficients of $Q(x)$.

This can be bashed out without the quadratic formula or with Vieta’s formulas, but the clever solution is much simpler:

Because $Q$ is monic,
$Q(x) = (x - (r+1))(x - (s+1))$
$= ((x - 1) - r)((x - 1) - s) = P(x-1)$. The sum of the coefficients of $Q(x)$ is $Q(1) = P(0) = 2010$.

Together with the clever tricks, ARML imposes a short time limit on its tests, making it difficult for contestants to finish the team and individual tests. The relay round’s three-minute and six-minute time limits provides a further emphasis on speed. As a result, ARML problems (with the exception of the proof-based Power Question) are usually not very hard mathematically; they’re just hard to do under severe time pressure. This short time limit, along with the small number of questions on ARML, make the results of the contest subject to a lot of random noise. The top teams are usually within a few points (out of 300 points total) of each other, so a five-point team round problem could easily change a team’s ranking by several places. The individual round has only ten problems, so achieving a national high score (usually at least eight problems) requires making no computational errors. Thus, the list of individual high scorers is somewhat meaningless; high scorers often do not repeat as high scorers when they return, and high individual scorers are often as much a result of luck as of mathematical ability.

Evaluating ARML based on the criteria that I listed in my post on Contest Math, we obtain mixed results. ARML, perhaps more than any other contest, highlights the social side of mathematics and hooks people into liking and doing math; though it’s hard to start doing ARML, it’s even harder to stop. Mathematically, though ARML does reinforce the importance of creativity, it does not give particularly challenging problems, and ARML results do not really constitute a good measure of mathematical achievement.

I enjoy ARML primarily based on the social part of the contest, and many people agree with me; the highlight of ARML for some people is the long bus ride to the contest. Indeed, I think of ARML primarily as a social event, with some mathematics to make it look like the participants are actually doing something important.

May 24, 2010:
“What does a water heater do? Does it heat water?” — Moor

May 25, 2010:
“Cutting hair takes longer than growing hair.” — Moor, talking about harvesting hair. He seems confused.

May 26, 2010:
Contributed by Ben from a bridge game.

• “If I open 2 no-clubs….” — Eric
• “Weapons and swords are very different!!” — Matt
• “I’m NOT an analogy!” — Ben

May 28, 2010:
Contributed by Ben from another bridge game.
“I don’t care if it converges… Just sum it!” — Eric

June 2, 2010:

• “Do airlines provide transportation?” — Moor
• “Apparently, straws bend.” — Moor

Apparently, Moor needs a lesson on common sense.

June 7, 2010:

• “It shouldn’t be ethical to have English majors.” — Moor (commenting that English majors don’t seem to contribute as much to society as engineers)
• “Kangaroos and penguins are both birds.” — Moor
• “Penguins are mammals.” — Anand
• “All the Republicans have guns, so they’ll prevent you from eating them.” — Anand