Teachable Moment: The Fibonacci sequence is a great introduction to math in nature and this little trick even provides a nifty practical use of the numbers.
From the blog: "The Fibonacci sequence is made up of numbers that are the sum of the previous two numbers in the sequence, starting with 0 and 1. It's 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144… 1 is 0+1, 2 is 1+1, 3 is 1+12, 5 is 2+3, and 8 is 3+5. The number after 144 is 233, or 89+144. The Fibonacci number describes the golden spiral, an ideal form much beloved by designers everywhere. Interestingly, it also neatly matches the relationship between kilometers and miles. Three miles is five kilometers, five miles is eight kilometers, eight miles is 13 kilometers. It's not perfect, eight miles is actually 12.875 kilometers, but it's close enough in a pinch. If you need to convert a number that's not on the Fibonacci sequence, you can just break out the Fibonacci numbers, convert, and add the answers. For instance, 100 can be broken down into 89 + 8 + 3, all Fibonacci numbers. The next numbers are 144, 13, and 5, which add up to 162. 100 miles is actually equal to 160.934. Again, close enough. Math is cool."