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Comment by yegle | Hacker News Reader

Call me snarky but instead of just multiply/devide by 1.6, you rather prefer remembering the Fibonacci numbers up to, I don't know, 200 to be useful?

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In practice, at least in my experience, only up to 13. (Though, I have the sequence memorized up to 21 because of a sign outside Chattanooga[0], which is what gave me my "hey, wait" moment about this.)

A combination of both the fundamental theorem of algebra and Zeckendorf's theorem has allowed me to fill in the rest so far. For example, 25 mi = 5 * 5 mi, which yields 5 * 8 km = 40 km. As it turns out, that is how far Cleveland, TN, lies from Chattanooga.

0: https://usma.org/metric-signs/tennessee

>A combination of both the fundamental theorem of algebra and Zeckendorf's theorem

How do you apply the fundamental theorem of algebra here?

I will go out on a limb and assume they meant the fundamental theorem of arithmetic, that all numbers can be (uniquely) factored into primes.

The list isn't that long. 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, and 144.

I memorized this almost by accident. I was doing hand rolled spaced repetition system for conditioning myself to fix some bad habits, and they came up often enough that it was memorized.

Just spend a few sprints in a sufficiently dysfunctional agile team and you’ll learn all sorts of higher Fibonacci numbers.

Technically they could also also be functional teams with a long history of gradual point drift... Though most organizations shake teams up before then.

If a ding that gets mentioned in planning is 1 point and they regularly try to fit 144 point projects in a sprint without splitting it up, that's likely to be rather dysfunctional.

I mean it is possible that gradual point drift would get there. But sufficiently improbable that I know what I'm betting on.

For some reason we are using 20 instead of 21. I didn't even bother asking why

That is because fibonacci is used to indicate the ‘guess’timation part. 5 Instead of ‘twice as much work as a 2’ (4). The idea is when you get higher numbers the opposite happens: 21 sounds like a very specific number and not like a rough guess. 20 does.

So it becomes 1 2 3 5 8 13 20 40 inf ?

By that logic shouldn’t people just do 1 2 3 5 10 15 20?

Yes, but remembering the multiples of 10 is vastly easier: they are 10, 20, 30, 40, etc. Remembering the multiples of 16 is quite a lot easier: 16, 32, 48, 64 etc. You probably already know them.

Now to convert from miles to km replace a multiple of 10 by a multiple of 16. 70 mph becomes 112 km/h.

To convert in the opposite direction do the opposite. 130km/h is 128 km/h + 2 km/h = 80mph + 1 mph (rounding down since you don't want to have to justify this calculation at the side of the road, to a gendarme, in a foreign language).

1.6 km = 1 mile is just as accurate as using 1.618.., the golden ratio. (Enough for driving, not enough for space travel.) And using the Fibonacci method is less accurate than the golden ratio since small Fibonacci numbers are only approximately the golden ratio apart.

The only possible justifications for the Fibonacci method are:

1. You want people to know that you know what the Fibonacci sequence is.

2. You enjoy overengineering.

3. You're one of quite a few people who believe, for whatever reason, that the golden ratio appears all over the place like in measurements of people's belly buttons, the Great Pyramids, and so on, and that this has some spiritual or mathematical significance.

It's art. It's possibly not very useful (who knows, though?), but some will find beauty, joy, entertainment, surprise, amazement, incredulity, anger, disdain, indignation, fear, nostalgia in this. Others will feel the deepest and purest indifference.

I'm even lazier, 1.6 might be hard to do without a Calc, I just grab 50% of the original number, 10%, and then sum them to the original

That's how I do many kinds of percentages... like 72% is 50% and then 10% twice and then a couple of 1%s

In the same vein, converting pounds to kilos is "divide by 2, subtract 10%".

no way just discovered this lmao i now only need a similar thing for fahrenheit to c/viceversa, i'm sure it exists. however, i'm so lazy i will not search for that information now

For Celsius to Fahrenheit, just double it and add 30. It gets you pretty close for the temperature range that humans live in.

Here’s a practical solution based on this:

Take your kilometres e.g 60, divide by 5 -> 12, now times that by 3 -> 36.

Take your miles e.g 80, divide by 5 -> 16, times 8 -> 80 + 48 -> 128

So any conversion reasonable conversion can be done in your head with your 3, 5, and 8 times tables

Yea, and since it's the golden ratio, the division is roughly the same as multiply by 60%. So you can just remember to take 60% and add it to the original or treat it as the answer depending on if you're going to or from the smaller measurement.

That's what I was thinking. I good example of over-engineering though.

Some people think differently. Some methods click with some people, while making others think it's making it overly complicated. The new math drove people crazy. The concept of doing extra math by rounding a number up to a whole number, and then subtracting the diff seems like a lot of work, but is amazing when used frequently to do "in your head" type of work. That extra match can lead to an answer faster than traditional math

How often you drive 200mph??

I think it's more common to convert distances.

I consider any distance reachable with one tank of gas commonly used (so up to 400 miles).

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