I used to love it and love the challenge, but when my son from Norway looked at gas at $2.29/gallon and asked "What would that be in crowns per liter?" I immediately started scrambling to see if I could find a shortcut or a trick rather than trying to do it in my head by brute force while driving. In the the end, he pulled out his device and started doing the calculations that way. We finished at about the same time. I actually did get an answer of 6.7 NOK/L just before he did, but that seemed odd and I wondered if I had misplaced a decimal and it was really 67 NOK/L. I said "6.7," but I wasn't at all confident.
He said they spend about 16 NOK/L in Tromso, which would be about $5.50/gallon.
And I'm still not sure I got that right, but that sounds about right. But if it was really supposed to be 5.8 NOK/L and I got a denominator and numerator switched so that it was actually almost seven bucks a gallon I would believe that too. I don't much play with numbers anymore, and the knowledge slowly seeps away.