Some time ago I came across the trick that allows easy conversion of miles and kilometers (and also mph and km/h) using addition only. The trick uses the fact that the ratio of the Fibonacci numbers is very close to the conversion factor between miles and kilometers. This is an example of turning multiplication to addition in a similar manner to the use of logarithms in a slide rule . Firstly, the Fibonacci sequence is pretty easy to remember or regenerate from scratch because it is generated by the rule "the next number is the sum of the preceding two numbers". The sequence starts from 0 and 1 and then proceeds 1, 2, 3, 5, 8, 13, 21, 34, ... Each number is the sum of the previous two numbers. Secondly, the ratio of consecutive Fibonacci numbers gets closer and closer to 1.62 the larger the numbers get. For example, 3/2 = 1.5, 8/5 = 1.6, 13/8 = 1.63, 21/13 = 1.62, 34/21 = 1.62, ... Lastly, there are 1.61 kilometers in a mile. If you take the ratio of Fibonacci