Incorrect mpg

[RussTaylor]

Oh man, we're going to go around and around in circles.

"You drove 110 miles total and used 50L plus some unknown amount, it was more than 10L because you stopped at 10L. You have used 50L + X, the unknown amount"

It doesn't matter, you know how much it takes to return it to full, therefore you know how much you used. You drove and used it, and you filled it back up, you know how much you used by how much it took to fill up.

X + Y + Z is the sum of all the partial fill ups + the amount required to return it to full.

So we have a huge coke bottle (say 75ltrs), and it took an amount (doesn't matter) to fill it up. We now have a full coke bottle, this is our reference.

You drink some, a bit more, you don't know how much but to help this discussion we'll say 10ltrs. So you have 40ltrs in there, you don't know that. You do the same two more times, you use another 20ltrs and now you're down to 30ltrs. But you don't know any of these measurements, because it doesn't matter.

So you have your full - x - y - z.

You then put 5ltrs in.

You drive around some more, so Full - x - y - z + 5ltrs - a.

You drive some more, then partial fill up (10 ltrs) then drive some more. So Full - x - y - z + 5 - a - b + 10 - c.

By now you've no idea what you have, apart from whatever remains of your original tank + 15 ltrs.

You fill it up (returning to our reference), this tanks 55ltrs.

You now know x + y + z + a + b + c = 55ltrs + 15ltrs = 70ltrs.

I have a way of knowing, because I have TWO references, both times the tank was FULL.

I will know how much coke I have drunk as soon as I fill the coke bottle right to the top. The amount I drank is 10L + 20L + 30L + whatever it takes to return it to the top.