Friday, August 29, 2014

Point of Brew: Americans get 410 mpg; wow!


June 7, 2011 |

When odd sets of data come my way, I make something of a fetish of juggling the numbers. This mostly boils down to dividing one number into another, which is an ample stretch for my mathematical competence.

Simple division, however, can be a useful check on whether the data are nonsense or plausible. I suppose most of these numerical factoids are put out, online for example, in pursuit of the wow! factor.

At one time, a prominent basketball player estimated that he had bedded 10,000 women in his playing career. Wow! If we assume his playing career was 15 years, that represents two willing women per day, including Sundays and holidays, with no time off for good behavior — or perhaps even playing basketball.

Here are three sets of factoidal numbers;

By way of the Internet I learn that it takes a gallon of diesel fuel to move the Queen Mary 2 a distance of six inches; wow! Now it is true that this is one humungous heavy ship and can travel very fast (for a ship), so the number might seem reasonable on the face of it.

The information given, however, permits one to calculate the amount of fuel required to complete the North Atlantic crossing that the Queen Mary 2 was designed to do, i.e., the 3,423 miles from New York to Southampton.

Turns out that at the rate of 6 inches per gallon, the crossing would require in excess of 36 million gallons of diesel fuel, which, at something approaching $5 per gallon, represents a potential fuel surcharge of nearly $70,000 per passenger.

And we thought the airlines were pirates!

Another number I learned from a railroad company advertisement is that a railway engine can move one ton of freight 425 miles on one gallon of fuel; that is just 6 gallons per ton from New York to San Francisco. Wow! Now my car weighs about a ton; it can barely make it from here to Chico and back on that amount of gas.

I am sure both numbers in these two examples have been arrived at by some punctilious calculation, but there probably is an assumption in the calculation that we are not told about. For example, let us say it takes one gallon of fuel to move the QM for the first six inches of any journey, i.e., starting from rest. Maybe the freight train is coasting?

The third example has more to do with the general subject of this column and explains why these musings are here in the first place.

This example just arrived by way of email from a friend who forwards many interesting things and some very funny things as well as many really dumb things. I guess the world has two kinds of people: forwarders of cyber-nonsense and non-forwarders.

Be that as it may, the recently forwarded factoid, unlike the examples above, contains a demonstrable and egregious error. Here it is the wow! factoid:

“Americans walk 900 miles per year. They consume 22 gallons of alcohol per year. Therefore they get 41 mpg. I’m proud to be an American.”

Now, 900 miles per year is about 2.4 miles per day or maybe 5,000 strides; and so that number seems reasonable enough because it is about half the recommended amount of exercise Americans should get. On the other hand, 22 gallons of alcohol is 2,816 ounces per year or 7.7 ounces per day; this is roughly the amount of alcohol in a 12-pack of beer.

Though the brewing industry would love this kind of daily devotion to swallowing beer it seems an unlikely, indeed ludicrous, per capita number.

Even if we assume the reporter means 22 gallons of whiskey (i.e., not alcohol in its pure form but in its diluted beverage form) that’s still enough alcohol for a six-pack of beer for each person each day (still a brewer’s dream) or at least five shots of whiskey a day per each.

Turns out that the figure of 22 gallons of alcohol per person per year is wrong by a factor of 10. We go through about 2.2 gallons of alcohol per capita per year in this country, so the 12-pack of beer each suddenly becomes just a little more than one bottle of beer or half a shot of whiskey per day; that is enough to do each of us some good and no harm at all. And it has no wow! factor whatsoever.

On the other hand, if the original proponent of the calculation quoted above was proud to be an American when getting 41 miles per gallon, he must be positively bursting with hubris at the revised mileage of 410 miles per gallon of alcohol consumed.

On the subject of miles per gallon (the typical mpg by which the fuel efficiency of a car is rated), I have a revision to offer: miles per dollar or mp$. I find it instructive and a powerful incentive to think twice before starting the engine.

My car, on its very best behavior, will travel 30 miles per gallon; at $4 per gallon that is 7.5 mp$. A Prius, by contrast, covers at least 12 mp$ and a standard SUV probably manages barely 5 mp$.

And mp$, I assure you, contains no errors and no hidden assumptions. It’s just a factoid with a rather substantial wow! factor.

— Reach Michael Lewis at Comment on this column at





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