5 ms·
It's both easier and more accurate to multiply by 1.6
by learnstats2 7y ago
It's both easier and more accurate to multiply by 1.6
- mkagenius 7y agoNot if you just remember 3,5,8,13 . You do not need to remember all fibonacci numbers, just the above and rest you can multiple by 2,5,10 and get them
- phkahler 7y agoHow many km is 4 miles? That's not on the list of numbers.
- adtac 7y ago4 is the average of 3 and 5, so its km value is the average of 5 and 8 (assuming the Fibonacci series to be a geometric progression as described in the tweet). While I can do this for 4km, I can't for different values like 9km. I've done the multiply-by-1.6 thing often enough by now to be fast enough at it, so I'll likely be sticking to it. This is a cool trick nevertheless.
- OJFord 7y agoOr use them in combination: 9 is 8 + 1, so that's 8->13 + 1*1.6 = 14.6
- OJFord 7y ago8 -> 13 and halve it for 6.5? Or any other combination, but using a higher Fibonacci number is going to be more accurate than combining smaller ones. Or in this case, as it's only 1 off a Fibonacci number you can convert that one and add 1.6 without multiplying it by anything (multiplying by the 1 off).
- CapricornNoble 7y agoI would solve it mentally as 4 miles = 3 miles + 1 mile. 3 miles ~=5km 1 mile = 1.6km So 5km + 1.6km ~= 6.6km
- bena 7y agoJust under 7. Or 6.666... Because knowing a km is 3/5 of a mile is more useful. It follows that a mile is 5/3 of a km. From there it's basic math. 4 * 5 is 20. 20 / 3 is 6.666...
- jameshart 7y agoOr 5/8 of a mile if you want a more accurate approximation. Or 8/13. Or 13/21.
- furyofantares 7y agoFor me, I think it’s pretty close for the numbers that are right on, and multiplying is way easier for intermediate numbers. 50->80 is one beat in my brain, it’s basically immediate because I know the first many Fibonacci numbers. But multiplying by 1.6 is only two beats, it’s “add a half” and then “add a tenth”, each of which come just as automatically as recalling a two Fibonacci numbers. 50->75->80. For the in-between numbers, 1.6 seems way easier. 40->60->64 is much quicker for me than averaging 50 and 80.
- Elte 7y agoYeah times 1.6 isn't too hard right? Just add 50% and 10% in succession, very easy to do in your head. The other way around is trickier. I tend to divide by 8 (or /2/2/2) and multiply by 5, which is harder but still consists only of steps that are clearly defined in my head.
- ilikepi 7y agoYeah, converting via the 5/8 ratio is how I've always done it. I traveled to Florida a number of times as a kid, and for whatever reason I have a permanent memory of the speed limit signs showing "55 MPH / 88 KMH". It's weird what one's brain seems to fixate on sometimes...
- prawn 7y agoI thought the same. As Australians in the US for a few months recently, I'd regularly ask my 6-7yo son to convert miles to kilometres as a test - say, 53 miles into km. Multiply by eight and divide by five (or divide by five first in cases where that was quicker). He found it straightforward enough.
- specialist 7y agoNice. Wish I'd thought of that. FWIW, I played points based games like cribbage with my youngsters to better encourage mental maths.
- saalweachter 7y ago5 furlongs in a kilometer, 8 furlongs in a mile. Easy peasy.
- nxpnsv 7y agoBut that is not the mathematicians way...
- waynecochran 7y agoYes. 1.6 = (1 + 0.5 + 0.1). So just halve the number and add it to itself. Need more accuracy add 10%.