If you drive 10,000 miles a year on average and wanted to replace your old car with a new car for the purpose of using less gas, how would these choices be ranked where 1 is the best choice and 5 is the worst choice?

Old NEW

A. 22 mpg 24 mpg

B. 18 mpg 28 mpg

C. 16 mpg 20 mpg

D. 34 mpg 50 mpg

E. 42 mpg 48 mpg

I’m puzzled at what you are trying to get at. Car D gets 50mpg, so if there are no other considerations, that’s the car to get. The mileage of your old car is IRRELEVANT! In accounting terms, it’s a SUNK COST. The order of preference is therefore D,E,B,A,C.

If you want to brag about your mileage increase at the local saloon, then the highest percent increase will win the day, but it’s a meaningless figure.

The percent increase in fuel economy is equally irrelevant! It is the absolute number of the new car that counts. Trading a Hummer for a Corolla is not as good as trading a Corolla for a Prius.

Are these city or hwy miles. If city, then “e” is the best choice, if HWY, then “d” is the car of choice. although “E” Is pretty darn good. The others pale in comparison and shouldn’t even be considered.

I’d rank by percentage improvement best to worst: B,D,C,E,A

I also don’t get the point of the question. If I only drove 10K miles per year I wouldn’t be replacing any car due to it’s fuel mileage.

Oh, that is brilliant.

Clearly the answer is: B, C, D, A, E

D is best. The improvement from 34 mpg to 50 mpg would save you the most fuel per year.

`Most fuel quality or the largest percentage reduction?`

Many people are concerned with improving gas mileage of cars to reduce the impact of greenhouse gases on the environment. Assume that a person drives 10,000 miles per year and is contemplating changing from a current vehicle to a new one.

Rank the following changes in vehicles in terms of their benefit to the environment (i.e., which new car would reduce gas consumption the most compared to the amount used by the original car). Use 1 for the change that would reduce gas consumption the most compared to the original car, and 5 for the change that would reduce gas consumption the least compared to the original car.

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Vehicle Change
Original v. New car
A. 22 mpg 24 mpg ____
B. 18 mpg 28 mpg ____
C. 16 mpg 20 mpg ____
D. 34 mpg 50 mpg ____
E. 42 mpg 48 mpg ____
```

I enjoy puzzles with some useful purpose. To usefully answer your puzzle, the old car would have to be destroyed!! If your 18 mpg car ends up in the hands of a busy socialite on steroids, it will consume far more gas than it ever did in your hands, and the environment would suffer.

I sold my 8cyl. Caprice to a guy who likes old cars and does not drive much. So by buying a 4 cyl. Corolla I actually helped the environment.

Why?

Yes, this is a trick question. The way to solve it is to calculate gallons per 10,000 miles. That is, how much fuel will each of these ten cars require in a year’s time? Try it and you will see that upgrading old B to new B yields the greatest reduction in fuel requirements of each pair. Interesting!

Nothing tricky about the method; you have to know how much fuel per mile or 10,000 miles is used before & after. Of course, it’s B,C,D,A,E. But in my book you are only a hero if you go to the 50mpg car. Reducing your drinking from 10 bottles of beer a day to only 5 is a good first step, but you need to go to 1 bottle or stop drinking altogether.

It depends on your priorities. Is maximum mileage the goal or is improvement beyond the old car the goal? If it’s the latter, just divide new mileage by old mileage and order them from highest to lowest ratio.

To de-mystify this “Puzzler”

This was the topic of a recent paper in the Journal “Science” (Larrick and Soll, 20 June 2008, Science,Vol. 320, p.1593). They took a poll of people under various conditions, this question, in the second form, was one of those questions (see the supporting material to the article). The thing that they were pointing out is that the “important” factor in getting a more fuel efficient car is the amount of fuel consumed per average year of operation (i.e. 10,000 miles) The argument was to not consider fuel efficiency (MPG) but fuel consumption Gal / Miles or Gal / 100 miles for more reasonable numbers. When viewed this way, the distance traveled is fixed and the variable is in the denominator. Thus as MPG increases, the “benefit” of getting a more fuel efficient vehicle decreases. It is an exponential decay 1/MPG. So, for the world to do something, the message is to not preach to the choir. That is if we do manufacture cars that increase the lower end efficiencies for more people, the impact on energy consumption (cost and carbon emission) will be greater than if the smaller percentage of concerned people get super fuel efficient cars. The take home message is that manufacturers can make a significant difference with only a small effort and the public need not make any choice. The exponential drop is what is not normally intuitive to consumers.

How about the one that you park in the drive way and that you walk past on your way to work.

Do the following calculation for each case. Let Old be the miles per gallon for the old car and New the same figure for the new one. The savings in gallons per mile are 1/Old minus 1/New. You will need 4 decimal places for reasonable accuracy. (The first decimal place will be zero for each of your examples.) From biggest savings to smallest, the results are B (0.0198), C (0.0125), D (0.0094), A (0.0038) and E (0.0030). To extend the results to annual comsumption and cost, multiply the result by your annual driving distance (10k miles) and the price of fuel ($4 to $5 per gallon).

Unless you are mathematically sophisticated, you may be surprised by these results. The problem with measuring consumption in terms of distance per unit of fuel (miles per gallon) is that it is non-linear when you try to compare cars with different fuel consumption. Because of this effect, which is purely mathematical, huge differences in miles per gallon between fairly economical cars result in small differences in the amount of fuel actually consumed. It explains why going from 16 to 20 mpg saves more than going from 34 to 50 mpg.

We should, instead, be measuring fuel consumption in terms of fuel per unit distance. In countries that use the metric system, consumption is figured in liters per 100 kilometers. If we want to stick with gallons and miles, we should use gallons per 100 miles or 1,000 miles.

We should, instead, be measuring fuel consumption in terms of fuel per unit distance. In countries that use the metric system, consumption is figured in liters per 100 kilometers. If we want to stick with gallons and miles, we should use gallons per 100 miles or 1,000 miles.

Good point. While we are at it, why don’t we measure speed in hours per mile instead of miles per hour. Maybe seconds per mile would be more practical. By inverting the speed, it’s a lot easier to calculate how much time a trip will take and also it becomes a lot more obvious how little time you save by passing on the double yellow to get around someone who is only going 60 mph (60sec/mile) so that you can keep going 70 mph (51.4 sec/mile) all the way to your turnoff that is only one more mile away.

Have you ever noticed that all the people who drive like they’re on their way to a fire on the freeway don’t seem to be late enough to run to their cars in the parking lot? What would save you more time? going 80 for two miles instead of 70, or running instead of walking to the parking lot that’s 1/8 mile away?

I love it! What a great discussion…B.L.E. I wish people were imprinted with this kind of information at birth. I always get a kick out of the guy who is riding my bumper for miles, passes me on a double yellow risking his life and the lives of countless others…and then I find him just ahead of me at the next traffic light miles ahead of me. All of that recklessness to gain what, maybe 1 second??