That's pretty good. If you wait to fill up (with gasoline) a whole week it will cost $80 because your tank is empty.
But if you fill it up on Wednesday, it will only cost $20 because your tank is half full. So you can save $40 a week by filling it half full twice instead of full once.
I guess Shaq had trouble with math in school.
You laugh, but in my cars the half-way mark on the fuel gauge has often been reached before I actually used half the fuel. Don't know whether that's a safety margin feature or they just can't build gas tank gauge systems that work. (You know, like the right side mirrors that have stickers on them that say, "Don't trust me, I don't work right.")
So, maybe not that extreme, but filling the tank at the half way mark twice might actually be cheaper than filling it when it's empty. :)
But you still use the same amount of fuel every week!
Well, yes, of course! But we're not talking financial sense reality, we're talking objectively observed reality.
Let's say I fill up the tank at the 1/2 way mark, which is really the 60% full mark. I observe that it costs, let's say, $20 to fill up "half" a tank. I fill up half a tank everytime I hit that mark, but because I'm not actually tracking my fuel expenses, I have no real idea how much I'm spending in total on fuel.
But if I let the tank go empty, it might cost $50 to fill it up and THAT I'll remember, because it's more than twice $20!
(It's 1am and I'm not going to do the math on my $20, 40% fill-up. You get the idea.)
So, I'll easily observe and remember these two absolutely correct facts. And draw the wrong conclusion from them because I'm not tracking what actually matters -- total fuel cost.
It's kind of like the allied air force folks who observed where the bullet holes were in the planes that returned from combat with the enemy. The air force folks decided they needed more armor where the holes in the plane were.
That is, until a statistician explained to them that the planes they were seeing were the planes
that survived. They needed to put more armor in the areas that
didn't have holes in the surviving planes because those planes were the ones being shot down. 100% correct observations about where the holes were and the original assessment of what to armor was completely wrong.