131–140 of 208 posts
In related news - pounds to kilos is "divide by 2, less 10%". Very precise too. 160lbs = 80 - 8 = 72kg
So n * (1-0.5) * (1-0.1)... This could also work for miles to km conversion in a similar way: n * (1+0.5) * (1+0.1). Not as accurate as golden ratio but still acceptable. :D
1 mile = 1609 meters.
3.1 miles = 5 kilometers.
6.2 miles = 10 kilometers.
...
26 miles, 385 yards = 42.195 kilometers.
100 miles = 160.9 kilometers.
Sorry, that's as far as I've run.
I use a similar method of easy-to-remember numbers in conversion between celsius to Fahrenheit: 0 = 32 10 = 50 20 = 68 30 = 86 Then roughly, subtract/add two F for every extra C. It’s easy to remember 32 and 50, while 68 and 86 are reversed.
Just had a flashback - my mum giving me a comparably helpful mnemonic about four decades ago: 16 (c) ~= 61 (f).
That, along with human body temperature (38C ~= 98F) have stuck, and between them I can guesstimate most numbers in between on the foreign (F) scale.
I use a similar method of easy-to-remember numbers in conversion between celsius to Fahrenheit: 0 = 32 10 = 50 20 = 68 30 = 86 Then roughly, subtract/add two F for every extra C. It’s easy to remember 32 and 50, while 68 and 86 are reversed.
If you want to get fancy, you can call it the Taylor approximation. I'm a bit lazy so I try to use the F(c)= 2 * c + 32 approximation described in a sibling comment, but for the range of human-friendly temperatures the error is too big. The problem is not the absolute difference, but how each temperature feels. So I have to resort to making the exact calculation or using Google for the conversion. I'll try your metho…
Example: 22℃ -> 44 - 4 + 32 -> 72℉. (Exact is 71.6℉)
Example: 23℃ -> 46 - 5 + 32 -> 73℉. (Exact is 73.2℉)
I've seen people do the going back 10% before the doubling. That's fine if you are not going to round. If you are going to round, take off the 10% after the doubling or you could end up off by up to 1℉ for the final rounded amount.
For example, 26℃ with rounding after -> 52 - 5 + 32 = 79℉ (78.8℉ exact). With rounding before it goes -> (26 - 3) + 32 = 78℉.
Earlier quoted context omitted.
don't they still use pounds per square inch ? Now, in Europe (excluding the UK) they also still use some weird units from the past. Calories for example, and horse (!!) power.
We still use PSI for tyre pressures in UK, probably some other things too. They're given in N/m^2, but all the petrol station machines are in PSI, probably because the numbers just fall better.
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I never bought this argument, but I'm not confident about it. Isn't base 10 inherently intuitive because of the obvious reasons? IE an order of magnitude is just another 0? Since I learned about base 2, etc, long ago, I always thought there was something magically elegant about base10 and never understood this? The explanation I've always heard, being 10 fingere, doesn't seem to explain all the elegance with base 10…
In base 8 (if we'd had 8 fingers), an "order of magnitude" would have been defined as "times 8" instead of "times 10", so it would also be adding another 0. Same with base 12. Base 16 would have the further advantage that we could easily halve, quarter, eighth, or 16th any number ending in 0 to a whole integer (in base 10, we can only halve, fifth, or tenth).
Earlier quoted context omitted.
We still use PSI for tyre pressures in UK, probably some other things too. They're given in N/m^2, but all the petrol station machines are in PSI, probably because the numbers just fall better.
I thought they were given in bars instead of N/m^2.
Isn't that rather the physicists way? Works well enough, used in a way not quite as intended by mathematicians, ... Disclaimer: I am physicist myself.
Ha, I saw a downvote there! I'm fine with that - on the condition that you never, ever treat a differential operator like a fraction again ;)