There's a natural antipathy between numbers and me. Try as I might, I don't understand them, and they do their best to trip me up whenever possible. Every time I think I have a handle on the slippery devils, they outwit me one way or another. Luckily, when traveling, I don't have to pin them down exactly in two areas; I'm not a stickler when it comes to mileage or temperature. If I can convert kilometers or Celsius in an easy-to-remember way and come relatively close to the actual number, that's good enough for me. That's why I'm a fan of the “close enough” method.
Here's how it works. To convert kilometers into miles, I multiply the kilometers by six and drop the last digit. So, 50 kilometers times 6 equals 300. Drop the last digit and the answer is 30 miles. (If you went through a more complicated math equation, the absolutely correct answer, as opposed to the “close enough” answer, would be 31.06 miles.) If you've got 120 kilometers to drive before dinner, multiply 120 by 6 and get 720. Drop the last digit, and you realize you'll be stopping after only 72 miles (actually 74.56 miles). Doesn't that sound better than 120 km?
The same approach works when converting Celsius temperatures to Fahrenheit. You could opt for an elaborate mathematical formula, which you'd never remember, or use “close enough.” With my method, you double the Celsius number and add 32. So, 20 C doubled is 40 and when you add 32, the final answer is 72 F (Actually, if you used the complicated formula, the answer is 68 F.); 25 C becomes 82 F (actually 77 F); and 30 C is 92 F (actually 86 F). What's most interesting about this approach is that the method yields more accurate results in the lower range when it is imperative that you know the true temperature so you can dress appropriately, and less accurate temperatures when you are in the comfortable temperature range above 70F and won't suffer if you forget your sweater!
This “close enough” method has worked for me in Mexico as well as Europe. Now, if only my bank would appreciate this approach to checkbook balancing, I'd be a completely happy woman!