I remember doing something like this in high school, but we certainly used $1 bills instead of $100 bills. These guys had more confidence than we did back then. Check it out:

Video: burning a $100 bill

The key to the whole experiment is having an alcohol-water mixture: the alcohol burns and the water absorbs the heat. There are more details in this article.

I had been looking for a decent set of earplugs, and I ended up getting Etymotic earplugs a while ago after a friend recommended them. I was won over by the good reviews and the fact they are reusable instead of one-time use.

They run about $13 and they work great. The earplugs block out ambient noise but I can still hear people when they want to talk to me.

I stash these ear plugs in my jacket or travel bag so I remember to bring them with me when I go out.

Hearing loss can be avoided

According to the National Institute of Health (NIH), hearing loss from loud noises is completely preventable. Still, the NIH estimates nearly 15 percent of Americans between the ages of 20 to 69 have noise induced hearing loss.

My opinion: avoid loud places. But if you regularly go to loud bars/clubs/concerts, buy good earplugs and wear them. It’s well worth the few dollars you’ll spend to have hearing protection. Your future self will definitely thank you.

More about noise-induced hearing loss: article from NIH about hearing loss

Do you or your friends wear earplugs? What brands do you recommend?

Destination elevators do not have buttons inside the elevator. Instead, they work like this: you request your floor on the outside, and a routing system tells you which elevator to enter.

Since the elevators are less common, they have instructions, as follows:

The idea is that rather than having people crowd into an elevator and then request their floors, the destination elevators do the math before hand, and group people going to the same floors. This leads to fewer stops and time savings.

They are advertised to have up to a 30 percent time savings, according to the manufacturer.

Here is how the manufacterer describes the advantage of its Miconic 10 destination algorithm over conventional elevators:

(see page 7 of this document for full-size image)

If you want to see the elevator in action, you can check out this Youtube video of the Miconic 10.

Video: Schindler Miconic 10 Traction elevators

(I should mention this guy seems overly excited for his first Miconic 10 experience. But then it made sense when I saw his profile which claims “elevator photography since 1993,” which is quite the passion.)

We were deciding between getting individual 9 inch pizzas at $7 a piece, or splitting a couple of medium 14 inch at $14 a piece.

For fun, I wanted to know which pizza was a better value in terms of total area (as is customary, the size refers to the diameter of the pizza). Usually it is the case that larger pizzas are better values, but it is not always the case, so I like to verify.

As I was slowly making the calculation on my cell phone calculator, my friend quickly calculated the 14 inch pizzas were a better deal.

How did he figure it out so fast? Here’s the neat trick he used.

The mental math my friend did

My friend used the following logic: he would compare the ratio of the cost to the ratio of the pizza size.

The ratio of cost is easy: the medium pizza is 2 times as expensive (14/7).

The question is: do you get more or less than 2 times pizza? Rather than think about circular areas and radii, my friend compared the ratio of diameters squared:

Ratio of areas = (14/9)² = (1 + 5/9)² = (1.55…)² > (1.5)² = 2.25

My friend explained that for 2 times the cost, you are getting more than 2.25 the amount of pizza. Therefore, the medium is a better value.

(Now I’ll admit, the above calculation relies on some other tricks too, like knowing 5/9 is 0.555… (similar trick for other integers from 1 to 8: like 4/9 is 0.4444), and knowing that 15 squared is 225. But I’d hope that arithmetic is part of one’s civic education).

Why does the trick work?

The textbook way to solve the problem is to compute the total areas of each pizza, and then compare the ratio of the areas.

But when you take the ratio of two areas, certain terms will cancel out, like the factor of π. Additionally, there’s no need to calculate the radius of each pizza and then divide: the factor of 1/2 on the diameter also cancels out.

Here is a proof of why the ratio of diameters squared is the same as the ratio of areas squared. Let’s say the larger pizza has radius R and diameter D versus the smaller pizza has radius r and diameter d

So there you go, the ratio of the diameters squared is the same as that of the total areas.

Long way to solve the problem

Here’s the way I was goign to solve the problem in three steps:

1. Figure out the radius of each pizza (d / 2)
2. Calculate the area each pizza, but ignore the π term (r²)
3. Calculate the unit cost of each pizza (cost/area)
4. Compare the unit costs

This method will give the same exact answer, of course, but it takes a lot more time and gives precision that is not necessary.

It’s tempting, but it’s a habit that you might want to reconsider. As miserable as it is outside, you are probably better off facing the cold than facing the risk of a refueling fire. (Edit: a couple of comments have pointed out how rare this fire is. I should rephrase: it’s your choice whether to face the cold or the small risk of a fire)

The problem is that re-entering your car encourages static charge buildup, which can ignite gasoline vapors at the pump.

Here’s a video that demonstrates a refueling fire:

Video: refueling fire

(Okay, so I admittedly had a good laugh at how excessively she’s rubbing her sweater, as if she were planning on creating a fire. But then I figured we probably do these kinds of things unconsciously, especially during something as routine as filling up gas).

This information comes from the Petroleum Equipment Institute.

PEI has an educational campaign called StopStatic to educate people about the dangers of refeuling fires caused by static electricity.

The three tips they have are:

1. Turn off your engine
2. Don’t smoke
3. Never re-enter your vehicle while refueling

And by the way, cell phones do not seem to pose a risk of refueling fires, according to a comprehensive report by PEI.

So be safe this winter and stay outside when filling up gas.