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Cool math trick: Converting between miles and kilometers
Here's a very cool trick for using math to convert between miles and kilometers.
Tue, Aug 16 2011 at 11:28 PM
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Photo: Try Stan/Flickr
The Fibonacci sequence is made up of numbers that are the sum of the previous two numbers in the sequence, starting with 0 and 1.
It's 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144…
1 is 0+1, 2 is 1+1, 3 is 1+12, 5 is 2+3, and 8 is 3+5. The number after 144 is 233, or 89+144.
The Fibonacci number describes the golden spiral, an ideal form much beloved by designers everywhere. Interestingly, it also neatly matches the relationship between kilometers and miles. Three miles is five kilometers, five miles is eight kilometers, eight miles is 13 kilometers. It's not perfect, eight miles is actually 12.875 kilometers, but it's close enough in a pinch.
If you need to convert a number that's not on the Fibonacci sequence, you can just break out the Fibonacci numbers, convert, and add the answers. For instance, 100 can be broken down into 89 + 8 + 3, all Fibonacci numbers. The next numbers are 144, 13, and 5, which add up to 162. 100 miles is actually equal to 160.934. Again, close enough.
Math is cool.
Edit: I made a typo on 1+1=3. Thanks to reader Erlinda for catching it.
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Easiest trick is remember 0.6
From miles to km, add 0.6 more. 50 -> 50 + 30 = 80
From km to miles, multiply by 0.6. 80 -> 80 x 0.6 = 48
Easy-peasy and you are within 3%
I don't understand it.
It's fun, not useful. It relies on the fact that the next Fibonacci number divided by the this one tends to 1.61803... while a mile is 1.609344 kilometers. Because those numbers are close, the (for example) 4th Fibonacci number in miles is pretty close to the 5th Fibonacci number in kilometers.
so I'm at a local bar last night and get into a conversation with a pretty little woman. I tell her about this conversion trick and next thing I know she's like wow and can't believe how cool I am. Next thing she is asking me to her place where she has a hot latina roommate and she is telling her friend about my math trick. lets just say I left with a smile from ear to ear
or you can just use the iphone app
seriously?? how pointless and dumb. If you need a proxy in a pinch as the article suggests (note his messy calculations don't even come up with the right answer), just use 1.5 as your base.
This is badly written, badly explained, and rather useless. It presupposes that you either have the fibonacci sequence memorized, or that you spend time trying to count it up in your head to the values you need. Anyone who can do that can just multiply or divide by 1.6 instead and be done with it. It's only a cool math trick if it makes things EASIER. This does nothing of the sort.
I swear it just takes like 30 seconds to do the numbers up to about 240 odd.
Curious. Didn't find this badly written, explained or useless. While I may not readily know the Fibonacci sequence out to the realm of 4 digit numbers, this method seems perfectly viable and helpful as a mnemonic for distances below 100.
If you're enough of a geek to have the Fibonacci sequence memorized, you're enough of a geek to be able to manually multiply by 1.6.
SAE is the Society of Automotive Engineers. This is a large and important and politically powerful institution in America. If the SAE embraced the metric system then we would use the metric system. So far the reverse has been true.
Yet another indication of how idiotic the Carter administration was, he was the one who wimped out when we were supposed to toss SAE and go with metric.
Only because Detroit rather selfishly didn't want the one-time conversion expense.
America was ready to go metric in the 80s.
Metric is superior to English in every way.
UGH!!!
Another cool conversion math trick I discovered: to convert Celsius degrees to Farenheit, just multiply by two and add 30. You'll be within a couple of degrees at any temperature you're likely to experience. To go the other way (F to C), just subtract 30 and divide by two. WAY easier than multiplying by 9/5 (or is that 5/9? and adding/subtracting 32.
I prefer the accurate 'add 40, multiply by either 9/5 (C->F) or 5/9 (F->C), then subtract the 40 out'. It's the same idea as the 'standard' one except you're using -40F = -40C instead of 32F = 0C. Same as using 1.609 on a calculator or slide rule to switch between km and miles or back.
9C = 5F - 160
That doesn't really work. Sure you get close with 0 degrees C, but that is about it.
In fact, at one point, F and C are the same temperature. It is around -40 or something like that.
Yeah, I always love it when americans ask how cold it is in the winter here in northern Sweden, and I can tell them without having to convert.
or you could just give up the ridiculous Imperial system and use metric! Like the rest of the world. I mean really... this whole debate is ... stupid.
i think the 'divide by 5, multiply by 8' trick is far easier than memorizing the fibonacci sequence, tho i suppose the above method is probably quicker for small enough numbers or for somebody who already has the sequence memorized
The relationship isn't exactly coincidental. 1 km = 0.625 miles. As the fibbonacci sequence gets further out, the ratio of two terms in a row is 0.618. That's why you'll get an approximate answer. That is, f(n) / f(n+1) = 0.618, where f(n) represents the nth fibbonacci number.
Another example of how math is just a made up science that conveniently works out.
Funny, I thought science was just a made up application of maths that conveniently works out.
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