Is it 55 cents? I really need to learn how to use a calculator.

If you want to know the answer to something per other thing you divide the one by the other. So here, you want to know dollars per mile, so you divide 20 by 110, giving approx. 0.18 (i.e. 18 cents) as the answer.

That's it! I was doing it backwards. Thanks so much for the remedial 4th grade division lesson ;)

Mr Misteraitch, do you, by any chance, have a Midlands accent? Most of them would work, but I was hoping something like Blackburn. Never mind if you don't, but it would be nice if you did.
Yours,

Alas no, GeckoDundee, my accent is a somewhat neutralized South-Wales-Valleys one, with the odd overlay of East-coast Canadian, courtesy of my wife, and perhaps even the occasional Swedish note, seeing as how I’ve been living in a Scandinavian backwater for six years now…

I always always look at the units. You have something in dollars and something in miles, and the thing you want to know is in $/mi. So just put the $ over the mi. And if you have a fractional unit (say you started out with $/mi), just remember that the denominator of the denominator goes on top. So if you wanted to know the number of miles, you'd know the only way to get the unit on the bottom (mi) to the top is to divide by $/mi.

It's an old habit from my days as a physicist; I was taught to ignore the numbers until the units make sense.

Anytime a student would answer a question without units, my HS physics teacher would say "9.8 what? Water buffalo?"

I always always look at the units.

Me too, Eideteker. I can't really do formulae, I just work it out with the units. Which means that every single goddamn person in the lab comes to me to check their calculations, because while I'm slower, I'm also always right.

9.8 water/buffalo², actually.

while I'm slower, I'm also always right.

Me too; that's always been my deal. Slower, but always right, since grade school. At least you have a plausible excuse!

was the truck's tank completely empty before it was filled up with the $20 of gas? This could alter the answer...

Anytime a student would answer a question without units, my HS physics teacher would say "9.8 what? Water buffalo?"
Ha! My maths teacher used to say the exact same thing.

Misteraitch, while it wasn't the accent I was imagining when I read it, South Wales would work really well too. (Now I'm going to spend all day wondering what that would sound like with a dash of Canajan & Swedish).

(And isn't the Water Buffalo a metric measurement? Shouldn't it be in Bison?).