## Posts tagged ‘Fermi’

### No Bull — This is My New Favorite Fermi Question

It’s hard to say which emotion was strongest — awe, bewilderment, admiration, horror, fear — when I heard the following statistic:

McDonald’s sells 75 hamburgers every second.

But I’m a math guy, so there’s no doubt where my mind turned after that emotion passed:

How many cows is that?

Have at it, internet.

What do you get when you divide the circumference of a bovine by its diameter?

Cow pi.What is the favorite course at Bovine College?

Cowculus.A mathematician counted 196 cows in the field. But when he rounded them up, he got 200.

### Let Me Pencil You In

Pencils are infintely useful yet ridiculously simple — just a cylindrical piece of graphite surrounded by a hexagonal wooden sheath.

Well, typically.

Pencils come in all shapes and sizes, actually. They often have hexagonal cross sections, though some are octagonal, rectangular, circular, and oval.

Heck, there are even pentagonal pencils…

Which has to make you wonder, do we really need pencils in such a wide variety of shapes?

The answer may be no, but there is a practical reason for the multitude of cross sections. Can you think of any possible benefits that a rectangular pencil would have over a circular one, or vice versa?

The following problem about a pencil comes from Peter Winkler’s *Mathematical Mind-Benders*:

A pencil with pentagonal cross-section has a maker’s logo imprinted on one of its five faces. If the pencil is rolled on the table, what is the probability that it stops with the logo facing up?

And here’s a good Fermi question:

How many pencils are there in the world?

I have no idea what the answer is, but one respondent to this question on www.answers.com said, “42,462,013,000,000,000 pencils about.” The amazing part is that **17 people found this useful**!

Slightly less ambiguous is this question:

How many pencils were used to make this sculpture by George Hart?

Or maybe you prefer selected-response items…

Which of the following is the best estimate for the length of a continuous line that could be drawn using a standard pencil?

- 0.35 mile
- 3.50 miles
- 35.0 miles
- 350 miles

Or maybe you’re tired of all these questions. You didn’t come here for a quiz. You came here for some jokes. Fine.

Did you hear about the constipated mathematician?

He worked it out with a pencil.What kind of pencil?

A #2 pencil, of course!What’s the largest pencil in the world?

Pennsylvania.

If you’d like to learn more about pencils and their history — and, let’s be honest, who wouldn’t — you can **download a free copy** of Every Pencil is a Sandwich. In return, you’ll be asked to sign up for the pencils.com newsletter. If you love pencils and use them as much as I do, receiving the newsletter will be a treat, not a burden!

### Money-Saving Fermi Questions

I was pissed when my cousin wouldn’t give me two $5 bills for a $10 bill.

“Sorry, can’t,” he replied simply.

When asked why the hell not — I knew he had two $5 bills, because he had gotten one from the gas station attendant earlier, and the waitress just brought him another — he explained that all $5 bills are put into savings.

“When I receive a $5 bill, I don’t spend it. It stays in my wallet till I get home, and then it goes right into the piggy bank,” he said. “Every couple months, I take those bills to the bank. It’s an easy way to build up my savings account.”

“So, what, you save like $50 a year this way?”

“It’s a helluva lot more than you’d think,” he replied.

As stupid as this sounds, now **everyone** in my family is doing it. It is a low-impact way to build up your savings account. And it leads to a great Fermi question:

- If all of your $5 bills go into savings, how much will you save in a year?

And for my sons, who don’t often pay for things with bills large enough to require $5 in change, we have the following:

- If all of your nickels go into savings, how much will you save in a year?

**Fermi questions** are questions that require quantitative estimates to arrive at an answer. It often requires making assumptions, because exact data is unavailable. Here are a few others:

- What percent of people who have ever lived are currently alive?
- How many hot dogs are sold at Yankee Stadium during a baseball season?
- How long would it take a snail to travel from Miami to Los Angeles?
- What is the weight of a million dollars? (Assume 1,000,000 one-dollar bills.)

My favorite Fermi question is based on a Dunkin Donuts radio advertisement, in which they boasted:

We reject more than one million pounds of coffee beans a year.

Which has to make you wonder:

- How picky are they, really?