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This relates to another mathematical "oddity". Some regions in the EU measure fuel economy with km/l, while others measure in l/100km. Years ago, when the EU fi

This relates to another mathematical "oddity". Some regions in the EU measure fuel economy with km/l, while others measure in l/100km. Years ago, when the EU first released fleet fuel economy standards, there was a bit of confusion as some manufacturers averaged the fuel economy of their fleet and then converted to the appropriate units. Which gives a different result than converting to the appropriate units and then averaging.

russdill 8y ago
Incidentally, inverting your mpg figures to gpm actually makes your conundrum much clearer and helps to explain why many countries use the latter. 100 / 10 = 10 100 / 12 = 8⅓ 10 - 8⅓ = 1⅔ 100 / 30 = 3⅓ 100 / 60 = 1⅔ 3⅓ - 1⅔ = 1⅔
- csours 8y ago
  Reformatting parent for readability: 100 / 10 = 10 gallons used 100 / 12 = 8⅓ gallons used 10 - 8⅓ = 1⅔ gallons saved --- 100 / 30 = 3⅓ gallons used 100 / 60 = 1⅔ gallons used 3⅓ - 1⅔ = 1⅔ gallons saved --- As a side note: I worked in the factory that make Chevy Tahoes when they started making 2 mode hybrids. The hybrids didn't make more highway mpg, but they improved city milage from 16 mpg to 20 mpg. One of the problems is that doesn't sound like much of an improvement, but it's actually 1 1/4 gallons saved per 100 miles. https://www.autotrader.com/car-news/chevy-tahoe-hybrid-great-idea-not-good-enough-260370 https://www.autotrader.com/car-news/chevy-tahoe-hybrid-great...
klodolph 8y ago
As much as I argue that fuel/distance is the correct way to measure things, given that the vast majority of people keep the distance they travel fixed as the amount of fuel and its cost fluctuates, it is a bit easier to do certain math with the distance/fuel metric. If I get 25 mpg and have a 12 gallon tank, that's 300 miles per tank. The nice thing about this is that it's a fixed value with simple, understandable units that more or less doesn't change as long as I keep the same car, presumably for many years. It helps me plan trips—I know that I regularly visit family who live 110 miles away, so anything with less than 220 miles to the tank forces me to refuel any time I see them… which affects my plans. America being less dense than Europe might partially explain why mpg is so popular here. A trip of 110 miles (or 200, 300) is not unusual in America. I remember making a series of trips to pick up a family member in college some 250 miles away, and that’s because she went to one of the closer options! The same problem (averaging reciprocals) shows up in investment. If you get 10% growth this year and 10% decline next year, the average is not (1.1 + 0.9)/2 = 1.0 = 0% growth, it is 2/(1/1.1 + 1/0.9) = 0.99 = 1% decline.
- Too 8y ago
  Most cars don't tell you how many gallons are left in the car, just approx how much of a full tank. So mpg doesn't help much in your example, miles per full tank is a useful number though and from there you can calculate that if you have half tank you only have 300/2=150 miles left. Though most cars will tell you the exact remaining distance to empty in the instrument cluster already so there is no need to do this mental arithmetic anyway.
  - Ntrails 8y ago
    As the owner of a very basic 2003 car, I can assure you that the mental arithmetic remains. I know that each 8th of my tank on the gauge is worth ~50 miles, entirely dependent on how efficiently I'm driving.

russdill 8y ago

Incidentally, inverting your mpg figures to gpm actually makes your conundrum much clearer and helps to explain why many countries use the latter. 100 / 10 = 10 100 / 12 = 8⅓ 10 - 8⅓ = 1⅔ 100 / 30 = 3⅓ 100 / 60 = 1⅔ 3⅓ - 1⅔ = 1⅔

csours 8y ago
Reformatting parent for readability: 100 / 10 = 10 gallons used 100 / 12 = 8⅓ gallons used 10 - 8⅓ = 1⅔ gallons saved --- 100 / 30 = 3⅓ gallons used 100 / 60 = 1⅔ gallons used 3⅓ - 1⅔ = 1⅔ gallons saved --- As a side note: I worked in the factory that make Chevy Tahoes when they started making 2 mode hybrids. The hybrids didn't make more highway mpg, but they improved city milage from 16 mpg to 20 mpg. One of the problems is that doesn't sound like much of an improvement, but it's actually 1 1/4 gallons saved per 100 miles. https://www.autotrader.com/car-news/chevy-tahoe-hybrid-great-idea-not-good-enough-260370 https://www.autotrader.com/car-news/chevy-tahoe-hybrid-great...

klodolph 8y ago

As much as I argue that fuel/distance is the correct way to measure things, given that the vast majority of people keep the distance they travel fixed as the amount of fuel and its cost fluctuates, it is a bit easier to do certain math with the distance/fuel metric. If I get 25 mpg and have a 12 gallon tank, that's 300 miles per tank. The nice thing about this is that it's a fixed value with simple, understandable units that more or less doesn't change as long as I keep the same car, presumably for many years. It helps me plan trips—I know that I regularly visit family who live 110 miles away, so anything with less than 220 miles to the tank forces me to refuel any time I see them… which affects my plans. America being less dense than Europe might partially explain why mpg is so popular here. A trip of 110 miles (or 200, 300) is not unusual in America. I remember making a series of trips to pick up a family member in college some 250 miles away, and that’s because she went to one of the closer options! The same problem (averaging reciprocals) shows up in investment. If you get 10% growth this year and 10% decline next year, the average is not (1.1 + 0.9)/2 = 1.0 = 0% growth, it is 2/(1/1.1 + 1/0.9) = 0.99 = 1% decline.

Too 8y ago
Most cars don't tell you how many gallons are left in the car, just approx how much of a full tank. So mpg doesn't help much in your example, miles per full tank is a useful number though and from there you can calculate that if you have half tank you only have 300/2=150 miles left. Though most cars will tell you the exact remaining distance to empty in the instrument cluster already so there is no need to do this mental arithmetic anyway.
- Ntrails 8y ago
  As the owner of a very basic 2003 car, I can assure you that the mental arithmetic remains. I know that each 8th of my tank on the gauge is worth ~50 miles, entirely dependent on how efficiently I'm driving.