Picture this: You’re a zealous acolyte of the metric system, with a rare affliction that makes multiplying decimal numbers impossible. You’re on holiday in the UK, where road signs give distances in miles. Heathens! How can you efficiently estimate the number of kilometres without multiplying by approximately 1.60934?

As it happens, such a method does exist. Remember Fibonacci sequences from high school, where the next term in the sequence can be computed by adding the previous two entries? The sequence starts with (1, 1, 2, 3, 5, 8, 13, 21, 34, 55…). Aside from being a really bad way of modelling a population of rabbits, which is what it was originally proposed for, the Fibonacci sequence has the property that the ratio of successive values converges to the Golden Ratio, the further down the sequence you go.

The Golden Ratio is approximately 1.618, which is rather close to the miles to kilometres conversion factor above. What does this mean? It means if we take a number of miles, decompose it as a sum of Fibonacci numbers, bump each Fibonacci number up to the next one in the sequence and add them all together, we get a good approximation for the number of kilometres.

Sound confusing? Let’s do an example. 60 miles is about 96.56km, and 60 = 34 + 21 + 5. Each of the terms in that sum is a Fibonacci number, so using the recipe described above, our estimate for the number of kilometres is 55 + 34 + 8 = 97. Not bad!

Militant utilitarians (and pretty much everyone else) would point out that it’s easier and more accurate to just look up the answer on Google. They’re probably right. On the other hand, you’ve now just learnt of another way to momentarily distract yourself the next time you’re crawling in traffic on the M42 to Kidderminster, and that’s not necessarily a bad thing.