For this post, you will need either a #2 pencil and piece of paper, or a calculator.
Your back, so let's get started! I just got a new truck a little while ago, it's an old 1970 F100. Due to it's age, it has some wear, and lots of time for ambitious folks with questionable mechanical skills/sense. One issue, is the fuel gauge only works part-time. After running out of gas a few times, I now keep a full can of gas, and check the mileage whenever I park.
This is where the math comes in-
I filled the tank at 37,581 miles. Yes, it would be fair to assume it isn't the first time it has seen 37k. I go to Wally world, and the fuel guage is working this trip. When I park, the mileage is 37,641, and the guage reads half full... Or half empty, depending on your own beliefs and outlook. But this is math, not philosophy.
Anyways, the tank holds 18 gallons. So, for the slower, or drunker, out there we have 37,641 minus 37,581, divided by 9 gallons.
I don't know which I should worry most about