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Comment by pkrumins | Hacker News Reader

The original question was how to convert 19 miles to km.

First decompose it into a sum of Fibonacci numbers:

        19 = 13 + 5 + 1

Then find the next Fibonacci number for each one of them:

        13 -> 21
        5  -> 8
        1  -> 2

Then sum them up to get the result in kilometers:

        21 + 8 + 2 = 31km

Which is within 1.36% of the correct answer (the correct answer is 30.57km.)

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Okay, but you could also say

    19 = 20 - 1

then multiply by 1.6

    20 -> 32
    1  -> 1.6

and get the estimate 19mi = 30.4km, which is even closer and seems rather easier to me than figuring out a set of Fibonacci numbers which sum to 19.

I thought the OP was alluding to the slight ambiguity because 1 appears twice in the Fibonacci sequence. You could interpret the approach two ways and do either 21 + 8 + 2 = 31 km or 21 + 8 + 1 = 30 km. Happily these span the correct answer of 30.55km.

In this situation I tend to pretend that 1 -> 1.5. (Or, indeed, 1.6, but generally that looks like claiming more accuracy than is really justified.)

Or you could do 21 - 2 -> 34 - 3

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