Thread: Calculating Average Fuel Consumption

Considering the amount of rubbish posted on the forum I thought this was very good. So there.

Many people record values such as these. Fill up with fuel and calculate the litres used per hundred kilometres.
They then work out the average for the whole trip. Obviously some people get it wrong. So... I thought this was very educational.

Of course, the easier way would be to work out the total distance travelled and the total fuel used for a trip and use those figures to get the overall fuel consumption.

The initial question was not very clear in relation to the supposed correct answer. We still need to hear back from the OP on which figure he/she wanted, average consumption or overall. "Average" as a word was misused here I think. If the OP was wanting 11.7 as the answer the word used should have been "overall", especially in light of the overall trip distance being given also.

Some of the name calling and attitude on this thread was not necessary at all...

I was always taught that you cannot take an average of an average.
Some of you need to go back to school.

Originally Posted by Brian

I was always taught that you cannot take an average of an average.
Some of you need to go back to school.

Quite right.

Averages of averages are meaningless figures, so there is no reason to think that the OP would want that.

If a group had 999 members who weighed 200 kg and 1 member who weighed 100 kg, would you seriously suggest that the average weight of the group was 150 kg?

If you did 999 km at 20 litres/100km and 1 km at 10 litres/100km, would you seriously suggest that the average consumption for the trip was 15 litres/100km?

While it might be possible to come up with some sort of semantic argument for assuming that the question required calculating the averages of the averages, that would assume that the OP was asking for a mathematically meaningless answer.

The only answer that makes any sort of mathematical sense is 11.7 litres/100km.

Well its obvious you werent driving a td5 disco, the fuel consumption is never that bad

Originally Posted by Brian

I was always taught that you cannot take an average of an average.
Some of you need to go back to school.

Originally Posted by vnx205

Quite right.

Averages of averages are meaningless figures, so there is no reason to think that the OP would want that.

The only answer that makes any sort of mathematical sense is 11.7 litres/100km.

Where does the "average of the averages" come into it?

The listed fuel consumption figures are not given as averages but are provided by the OP as overall fuel consumption rates for the legs of the trip as noted in the OP.

Originally Posted by RoverP6B
A person travels the following distances and records for each distance the following respective fuel consumption figures.

300km, 200km, 400km, 100km and 12l/100, 13l/100, 10l/100 and 15l/100

They are not given as average consumption figures therefore when averaging these they are not "averages of averages".

Please explain the logic of how you are assuming the "average of the averages" are being taken.

Originally Posted by RoverP6B

Here is little question on fuel consumption and calculating the average. As with all things mathematical, there is only one correct answer, so what do you think?

A person travels the following distances and records for each distance the following respective fuel consumption figures.

300km, 200km, 400km, 100km and 12l/100, 13l/100, 10l/100 and 15l/100.

What is the average fuel consumption for the trip? Please give your answer correct to one decimal place.

Ron.

Originally Posted by windsock

Where does the "average of the averages" come into it?

The listed fuel consumption figures are not given as averages but are provided by the OP as overall fuel consumption rates for the legs of the trip as noted in the OP.

They are not given as average consumption figures therefore when averaging these they are not "averages of averages".

Please explain the logic of how you are assuming the "average of the averages" are being taken.

The figure of 12 litres/100 km for the first 300 km of the trip is an average for the first 300 km. It is an average, because that is how the figure is calculated. All the driver knows is that she used 36 litres to cover the 300 km, so she calculated from those two figures that the average for that part of the trip was 12 litres/100 km.

It might not be labelled as an average, but it definitely is an average.
I am using average in the colloquial sense. It is really the mean, but I am continuing the terminology used by the OP in the hope of avoiding confusion.

Does that help?

Originally Posted by DEFENDERZOOK

going by the figures given above......the answer is 12.5 l/100......

to calculate the average......you add up the results and divide by the number of of results......
ie.....12+13+10+15 divided by 4.......=50 /4......=12.5

the kms given in the question are not required as the maths has already been done for each leg of the trip giving the average.....
so all thats left to do is work out the average of all the averages......which will give the final average.....

Each leg (Km/l) is an average.
So doing it this way above is an average of an average, and is meaningless.