You can use Fibonacci numbers to approximately convert miles to km

This is because fibonacci numbers approach golden ratio which is approximately 1,618033... and one mile is 1,609344 kilometres exactly.

🦅🦅🦅

Just gotta ask any of the 90% of the world who use it to find out. Americans hate this one simple trick!
- Fun fact: there's quite a lot of countries that use "mixed metrics", with no real rhyme or reason for what uses old ancient imperial and what uses new shiny metric
  UK - Miles for long distances, switch to meters for distances less than a mile, always use km in air and sea. Milk in pints, petrol in liters, water in ml, beer in pints. Human heights in Feet Inches, building heights in Meters. Human weights in a unit even Americans don't use anymore (Stone), animal weights in kg/g.
And yet the military uses "clicks"
0.54 nmi (nautical miles)

This is such a cool example of how some recursive algorithms have a closed form. We all know that there's a simple equation to plug miles into to get kilometers, but we don't talk about how the Fibonacci sequence has a closed form. This is so cool.

Wjat does closed form mean? Asking as a stupid botanist, sorry.
- Closed form means it can be written out as a specific, finite set of instructions that work the same regardless of what the input to your function is.
  For Fibonacci, it is most commonly defined in its recursive form:
  
  f(0) = 0 f(1) = 1 f(x) = f(x-1) + f(x-2) for integer x > 1
  But using this form, computing a very large Fibonacci number requires computing all the numbers before it, so it’s not the same finite set of instructions for every number, it takes more computation to generate larger numbers.
  However, there is a closed form formula for generating Fibonacci numbers. Using this formula, you can directly compute any large Fibonacci number without having to compute all those intermediate steps. It takes the same amount of work to compute any Fibonacci number.
  
  f(x) = (a^x - b^x)/√5 a = (1+√5)/2 b = (1-√5)/2
  (Note that a and b here are constants; I only wrote them separately to avoid a mess of nested parenthesis)
  For an example of something that doesn’t have a closed form, we do not know of a closed form for generating prime numbers. There are several known algorithms for generating the nth prime number, but they all depend on computing all the previous prime numbers, making it very difficult to compute very large prime numbers (in fact, how generating large primes is actually done is by making an educated guess and then checking that it’s actually prime). Discovering a closed form formula for prime numbers would have a huge impact on mathematics and cryptography.

To go from km to mi I always leaned “multiply by 6 and move the decimal one to the left”. So 6km is ~3.6mi. Or 10km is just about 6mi.

Yes. That uses the 3:5 ratio.
or add half and then 10% (because it’s 1.6km to the mile): easier than multiplying decimals or large numbers by 6, and the inverse is 0.6mi=1km so easy to remember both ways (same thing but don’t “add” just start from 0)
glad I did not learn conversion in school. Nobody uses miles where i live
Thank you, will definitely use this now on
Honestly divide by 5 and multiply by 8 usually isn't too difficult and just gives you the right answer.
I remember it by 200mph is 320kph.
I used to remember because space (Karman line) is 100km or 62mi up. I guess it helps to be a space nerd for that one. Kind of just figure 1.6 going the other way.

Interesting, but if I have to look up a conversion I’ll just look up the actual conversion rather than an approximation.

Why have brain when have computer
- thanks to "AI" being in everything more and more computers are starting to perform worse than brain
The point is you don't have to look it up. Fibonacci is really easy to compute in your head.

Ah yes, I always remember the Fibonacci sequence and totally wouldn't find it harder to calculate than just doing the conversion the regular way

/sarcasm

"Remember"? Do you also remember all the digits of π?
It's defined as F(0) = 0, F(1) = 1 and F(n) = F(n - 1) + F(n - 2). Which makes more sense than imperial units.
- Or I could just do 1.6 km ≈ 1 mile whenever I need to convert from the standard that I use, Metric, to Imperial
  Far far far simpler
  Edit: I'm not American, I use sensible units, SI Metric
  Edit edit: I do fully have dyscalcus, mostly only effects "scary" looking maths, so no, your suggestion doesn't help
- Which makes more sense than imperial units.
  But you'd only need to do the conversion if you started with imperial units.
But woudn't you only need the 3 = 5 part?

I always used "a little more than half".

isnt it easier to give them simple conversions 1mi=0.6km.

Might want to check your units.
- It's rough estimation, a deviation of anything less than 50% is accurate enough for that
  Edit: Ooh I thought you were trying to "um actually, it's 1.66", but I just realised they put 0.6 instead of 1.6
or for in your head maths: half + 10%
(though it’s 1km=0.6mi, 1mi=1.6km)

Works because ratio of km to miles is about the golden ratio.

I’m never going to visit the US or UK anyway.

US and Israel are the only places that still use Imperial. While older generations in Canada and UK will speak about weight in Imperial, the official unit system is Metric.
- The UK still uses miles for vehicle speed and road signs
- US and Israel are the only places that still use Imperial.
  But the US has a global business empire. So you'll see the Imperial/Metric conversions all over the planet.

What if i don't want to

That's the spirit.
Give it the ol college "why?"

Cool! I wish I would have known this in the 70's when Canada changed over from British Imperial units to the Metric system. Maybe this is the incentive needed to push the usa into the rest of the metric system world!

If every measurement being a factor of ten of a smaller or bigger unit isn't going to convince Americans of the ease of metric then the Fibonacci sequence isn't going to convince them.

5 to 8 is the far simpler pretty exact conversion.

my upvote made 420 upvotes, coincidence?

I learned it in middle school