
Can you solve Seth Godin's math problem?  - Chrisroad
http://sethgodin.typepad.com/seths_blog/2009/08/not-so-good-at-math.html
======
jws
If we americans worked in gallons/mile instead these sorts of decisions would
be obvious and intuitive. No one goes out with the goal of burning a gallon of
gas so measuring how many miles you can go by burning one is silly. mpg is the
reciprocal of what they want and people are bad at reciprocals.

I fixed his problem below:

    
    
      Suburbans: 23.5 liter/100km
      Priuseses:  4.7 liter/100km
    
      Suburban+: 18.0 liter/100km (save 5.5 liters)
      PriusPlus:  2.3 liter/100lm (save 2.4 liters)
    
      Would you rather save, 5.5 liters or 2.4 liters?
    

(And you don't have to "go metric", just using gallons/1000miles would do
fine.)

~~~
3pt14159
I live in Canada where we typically get both mpg and liter/100 km. I've found
that, almost universally, my friends that report mpg have less fuel efficient
cars than the ones that quote liters per 100 km when asked about a vehicle's
fuel efficiency.

I tend to think that one of the reasons that Americans tend to have less fuel
efficient cars is that when they are evaluating alternatives 9 mpg and 10 mpg
are "closer" or more equivalent than 47 mpg and 50 mpg. For example, if I go
out and buy a Truck in Canada I could either compare

Ford F150: 15.7 liters/100km (15 mpg) city, 11.2 liters/100km (21 mpg)
highway.

GMC Sierra 2500 4WD: 14.7 liters/100km (16 mpg) city, 11.76 liters/100km (20
mpg) highway.

With the Sierra, you are using a full liter less of gas during city driving at
the cost of only half a liter of highway driving, so unless I'm doing more
than 66% of my driving on highway like conditions, I should go with the
Sierra, but that information does not come across to gas conscious buyers that
use mpg.

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JimmyL
The root of the problem is that we shouldn't be thinking in miles per gallon -
we should be thinking in gallons per mile.

The follow-up problem is that average person think miles per gallon is linear
(as they would phrase it, "the difference between 1MPG and 2MPG is the same as
the difference between 60MPG and 61MPG") because they don't know any better,
whereas it's really an inverse/reciprocal relationship.

I wrote a more though explanation of this -
[http://www.daniellanger.com/blog/2009/08/miles-per-gallon-
vs...](http://www.daniellanger.com/blog/2009/08/miles-per-gallon-vs-gallons-
per-mile/) \- the last time MPG came up in discussion, when there was some
minor outrage over the Volt claiming 230MPG.

~~~
mmt
I'm going to agree with another commenter, however, that the "saving fuel"
premise is flawed.

Personally, I like MPG because it makes the range-on-a-tank-of-fuel
calculation much easier, and I care much more about range than about fuel
economy.

I was sad when it turned out the original Honda Insight didn't get 70MPG,
because, otherwise, it would have been interesting due to the 700 mile range.

~~~
JimmyL
I'm curious - why the fixation on range of a tank of gas?

If we're talking about serious off-road vehicles, then I can see why you'd
want to max out your range to make trip planning easier. But thinking of the
majority of drivers doing the majority of their driving (especially in cars
like a Honda Insight), they'd be hard-pressed to end up going somewhere that
didn't have a gas station at least every 200 miles.

~~~
roundsquare
I think its more useful for a lot of people. If you drive to work and back
every day, then you know how many miles you drive. So you can say "I need to
fill up my tank every week" or something, and you can figure out how much
money you need to spend each week. Its not about wondering if you can fill up
during a trip, but about how much you need to spend on gas.

~~~
JimmyL
Interesting - I would never have thought of doing my budgeting that way.

The way I do it is that I know my work commute is about 30KM, so about 150KM
per week, and that my Mazda has an average combined fuel efficiency of about
7L/100KM - meaning that my commute uses about 42L of fuel per month. I know
that gas costs around $0.96/L in this area at this time of year, so my
commuting costs about $40 per month in fuel.

I use this line in my budget, and hence pay less attention to exactly when I
refill my tank - and know that any amounts I spend on gas above this number
are somewhat discretionary.

------
mnemonicsloth
The premise is flawed. We start with: _Let's say your goal is to reduce
gasoline consumption._

And then we start talking about fuel efficiency. IIRC, though, it's pretty
well established in the economics literature that increasing fuel efficiency
doesn't reduce gas consumption much, if at all. Increased fuel efficiency
means lower effective gas prices, which people respond to by driving more.

The net effect is about the same level of fuel consumption, with more cars on
the road (i.e. more traffic and more accidents).

If you want to reduce gas consumption, you have to increase the price. Good
ways of doing this include taxing it, increasing demand for other stuff made
from petroleum, or reducing supply.

~~~
modoc
The problem with increasing the price of gas is you hurt the poor most of all.
Honestly, jacking up the price of gas isn't going to change my driving habits
at all, but doubling the cost of gas (for example) will absolutely impact the
budget of a lower income person who is commuting to work in an older car. They
can't afford a newer car, they can't afford to move closer into the city, and
there isn't public transportation available. They have no options other than
to cut back on things like food and braces for their kids, etc... (sure some
folks blow lots of money on cigs, big screen tvs, beer, etc... - but honestly
the majority of people who are just scraping by, are doing their best).

Figure out how to make it affordable (while being safe) for people to live
closer into major cities, and you'll have a real impact on gasoline usage.

~~~
roundsquare
Two things come to mind that might work: 1) Gas credits for the poor... but
this might be hard to get right. 2) Cheap public transportation. This won't
work everywhere, but I suspect it would work in big cities and their suburbs.

------
RiderOfGiraffes
I find the easiest thing to do is assume we drive some distance, then work out
how much gas is used.

If we drive 1300 miles the numbers all work out easily (because it's divisible
by 10, 50 100 and 13)

Suburbans get 10 mpg: 130 gallons

Priuses get 50 mpg: 26 gallons.

Suburbans @ 13 mpg: 100 gallons (30 gallons improvement)

New Prius @ 100 mpg: 13 gallons (13 gallons improvement)

So clearly the best thing to do is scrap all the Suburbans and replace each
with a newer style Prius.

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charliepark
This is a solved problem. Seth actually linked to my explanation of it.
[http://charliepark.tumblr.com/post/169016492/in-seth-
godins-...](http://charliepark.tumblr.com/post/169016492/in-seth-godins-post-
this-morning-he-talks-about)

------
apotheon
That would only be a "math problem" if it came with enough numbers to do some
calculations.

Oh, wait -- he's probably assuming that the only worthwhile metric in the
problem is fuel usage. Well, with _that_ requirement, it's easy. Hell, I've
even done the calculations for determining how long it would take to recoup my
losses if I bought a motorcycle and used that instead of a car with decent
fuel efficiency, given some assumptions about future gas prices, a while ago:

<http://sob.apotheon.org/?p=449>

------
anigbrowl
Here's a better solution: replace the suburbans with Priuses instead of buying
into Godin's tired, second-hand false dichotomy. Some of us are wired for
arithmetic, actually.

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rubinelli
It may look unintuitive, but it's just an optimmization problem. When you
optimize, you always begin with the most resource-intensive element, because
that's where most of the gains are.

------
known
If the goal is to reduce gasoline consumption I'd suggest

    
    
        * banning futures trading on oil world-wide.
        * provide free public transportation.

------
petercooper
m/10 - m/13 > m/50 - m/100

