The math isn't quite obvious to me, but if you go out camping and get 5 MPG on the way to the campground and turn around and get 10 MGP on the way back, your average MPG won't be 7.5 as you would expect. It's actually 6.67.In other words, you used two thirds of your fuel on the way up and one third on the way back.Which gets me to thinking, why don't we simply use fuel consumption (i.e. gallons per hundred miles) instead of miles per gallon? It would be much easier to compare mileage if we did so.On edit: I'm not complaining about fuel mileage at all. This is a theoretical situation, not an actual report of MPGs. I'm just commenting on how odd it is that you can't average MPGs together.On second edit: Some people seem to be thinking that I'm complaining about fuel mileage. I'm not. Really, I'm not complaining about fuel mileage. I agree, you shouldn't complain about fuel mileage and I really, truly would never complain about fuel mileage. I'm talking about math here and how you can't average MPG averages. It's a quirk of math only. That's my only point. Really, I swear. I am not complaining about actual fuel consumption of any recreational vehicle.

It's only confusing when you phrase it the way you did. If you say you drove 20 miles and used 3 gallons of fuel, what would your mileage be. Nothing confusing about it really, just if you phrase it to be confusing. Mileage is miles driven divided by fuel used. Nothing could be simpler.

We are used to MPG in America, while liters per 100 KM is common in Europe.I like MPG much better.If you are driving a $100,000+ vehicle, why worry about the $300 to fill the tank? You probably can save more or spend more by finding another insurance company. Do you complain about the $1,200 spent on insurance? Or only the amount spent on fuel?Camping RV's are a pure luxury. While I was living in my RV, it was more like a low cost housing system. I could live in my RV and stay in a RV park twice a month for much less money than I spent on living in my prior home. There I had a $265 homeowners association fee, and utilities around $85 a month. My motorhome was paid for, and my only expense was insurance, gas, and the occasional oil change. Propane was about 10 gallons every 6 weeks in the summer and 10 gallons every 3-4 weeks in the winter. I spent a lot of time in one location to keep mileage down. MPG was improved a lot by driving at 55 MPG, as I no longer needed to arrive by 5 pm, in order to get a good nights sleep and go to work the next morning.So I kept my expenses below $800 a month that I had spent on my old home mortgage. Good luck,Fred.

50 miles one way5 mpg going....used 10 gallons10 mpg coming back......used 5 gallons15 gallons used.....100 miles traveled------6.67 mpg round tripWhere/how do you come up with 7.5 mpg??Your math & thought process is flawed

He got the average of 7.5 because he was only addressing the numbers 5 and 10 rather than the actual fuel mileage.

Taking an average of averages is mathematically incorrect and almost always leads to a non-senssical answer.So the (5 MPG + 10 MPG)/2 giving the 7.75MPG is wrong. As OldBiscuit pointed out you need to back out the average to get to the original data sets and combine them to correctly calculate the true average.It's a bit like that old math puzzle: 3 men go to a hotel and rent a room for $30 where they each pay $10. The desk clerk realizes the room is only $25 so he sends the bellboy to their room with a $5 refund. The bellboy realizes he can't split the $5 evenly, so he pockets $2 and give each man $1 back. Now the men have each paid $9 for the room ($10 - the $1 they got back), for a total of $27 and the bellboy pocketed $2 for a grand total of $29. Where did the other $1 go?

What's the average of 5 MPG and 10 MPG? | Good Sam Community

70 Replies

noplace2
Explorer
Jul 23, 2015
frizzen wrote:
cameronpatentlaw wrote:
Actually, to be precise, we'd have to use calculus and take the derivative of a function at the time you are measuring the fuel consumption to determine the rate at which you are burning fuel. That function must take into account a lot of factors--wind vector, vehicle weight (which itself is continuously changing as fuel is burned), coefficient of friction between road and tires (which is also continuously changing based on road surface characteristics such as tire wear), road inclination or declination, moon location, as if it is overhead, it's gravity will slightly pull the coach up affecting the force of gravity from the earth pulling the coach down. The weight of Cheetos in the coach should not change the formula too much if they are eaten, except to the extent weight moves from the cabinet over the back wheels to the drivers' seat over the left front wheel. Physicists refer to the foregoing as Winnebago's equation. Cheers,

Mike era70x.com

You DO understand that the likelihood of more than 4 people here understanding what you just said is negligible, right?

There is a significant remainder. They just won't get it, or they'll pretend that they do. YOU are funny!
frizzen
Explorer
Jul 23, 2015
cameronpatentlaw wrote:
Actually, to be precise, we'd have to use calculus and take the derivative of a function at the time you are measuring the fuel consumption to determine the rate at which you are burning fuel. That function must take into account a lot of factors--wind vector, vehicle weight (which itself is continuously changing as fuel is burned), coefficient of friction between road and tires (which is also continuously changing based on road surface characteristics such as tire wear), road inclination or declination, moon location, as if it is overhead, it's gravity will slightly pull the coach up affecting the force of gravity from the earth pulling the coach down. The weight of Cheetos in the coach should not change the formula too much if they are eaten, except to the extent weight moves from the cabinet over the back wheels to the drivers' seat over the left front wheel. Physicists refer to the foregoing as Winnebago's equation. Cheers,
Mike era70x.com

So what's the Eigen value?
noplace2
Explorer
Jul 23, 2015
1,603.6 hours as a private pilot. Yes, if I ran out fuel up there it would be a problem, although not as insurmountable one as might be thought. The little guys that I fly can be landed virtually anywhere. Go ahead, ask me how I know that! :B Didn't run out of fuel, but I CAN tell you that a 172 ,properly controlled, will give you about 8 minutes to pick a landing spot with NO power. Bless her heart! Did not bruise a kernel in the adjacent corn field. Getting said aircraft out of that field (at their expense because they blessed MY heart for not wrecking THEIR airplane and not suing them (another issue) I netted from them 100 hours of flight time and that wasn't, (still isn't) chump change. I've used every dime of it.

And again, your mileage might vary, but you will still need to fuel when you are out of it and you will pay the going rate, OR you will stop moving on down the road. Your MPG just doesn't matter!
mileshuff
Explorer
Jul 22, 2015
nevadanick wrote:
Wouldnt gallons per hour be the most accurate way to track fuel use ?

If you are in an airplane then thats what pilots use.
fj12ryder
Explorer III
Jul 22, 2015
No.
nevadanick
Explorer
Jul 22, 2015
Wouldnt gallons per hour be the most accurate way to track fuel use ?
fj12ryder
Explorer III
Jul 22, 2015
Actually that isn't quite right but very close. In point of fact you'll get your best fuel mileage going east because you'll also get the speed of the earth's rotation too. :)
RoyB
Explorer II
Jul 22, 2015
I noticed no one here brought up the thought that driving NORTH uses more fuel then driving SOUTH here in NORTH AMERICA...

I guess going NORTH means you are going up hill all the time...

The same rule applies when you are going EAST or WEST due to the Earth spin...

I am like everyone else - I just go until I run down between 1/2 to 1/4 tank and fill up again...

The only time I get a big smile is going from Northern Neck VA to GATLINBURG TN on one tank of gas pulling my no-wind resistance POPUP trailer. My truck almost calculates the same gas mileage whether I am pulling my 4200LB loaded down POPUP trailer or not...

Roy Ken
toedtoes
Explorer III
Jul 22, 2015
I don't think threads like this cause people to leave the forum. I think threads like this are harmless fun.

The threads that cause people to leave are the ones that are filled with rudeness, personal attacks, etc.
OkSixpack
Explorer
Jul 22, 2015
fj12ryder wrote:
Why would they be frustrated at a thread unless they were forced to read it? And that presupposes the fact that no other forums have the same issues, i.e. silly threads.

This X2. I find these amusing, and they break up the monotony.
Jim