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Bob_Bane comments on Truly Part Of You - Less Wrong

59 Post author: Eliezer_Yudkowsky 21 November 2007 02:18AM

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Comment author: Bob_Bane 21 November 2007 12:52:50PM 13 points [-]

I make it a habit to learn as little as possible by rote, and just derive what I need when I need it.

Do realize that you're trading efficiency (as in speed of access in normal use) for that space saving in your brain. Memorizing stuff allows you to move on and save your mental deducing cycles for really new stuff.

Back when I was memorizing the multiplication tables, I noticed that

9 x N = 10 x (N-1) + (9 - (N-1))

That is, 9 x 8 = 70 + 2

So, I never memorized the 9's the same way I did all the other single digit multiplications. To this day I'm slightly slower doing math with the digit 9. The space/effort saving was worth it when I was 8 years old, but definitely not today.

Comment author: giambolvoe 23 December 2010 11:16:05PM 1 point [-]

I always do my 9x multiplications like this! We were taught this, though. I can't say I figured it out on my own.

Comment author: hamnox 23 January 2011 03:54:03AM 0 points [-]

I learned my nines like that too, except I think the teacher showed us that trick. Of the things I learned personally... My tricks were more about avoiding the numbers I didn't like than being efficient.

I could only ever remember how to add 8 to a number by adding ten and then subtracting two. I learned my 8 times tables by doubling the 4th multiple, and 7 by subtracting the base number from that. I suppose I only ever really memorized 2-6 and 12.

Comment author: Davorak 21 April 2011 03:31:45PM 0 points [-]

Knowing how to regenerate knowledge does not mean that you only store the information in it seed/compressed form. However if you need the room for new information you can do away with the flat storage and keep the seed form, knowing that you can regenerate it at will.

Comment author: Normal_Anomaly 20 May 2011 10:10:41PM 1 point [-]

I sure wish I could choose what gets deleted from memory that easily.

Comment author: Davorak 21 May 2011 12:36:16AM 0 points [-]

In my experience it is just a matter of not using the memory/skill/knowledge. I was not trying to imply it was a quick process.

Comment author: Ender 11 August 2011 04:11:09AM *  7 points [-]

There were actually a few times (in my elementary school education) when I didn't understand why certain techniques that the teacher taught were supposed to be helpful (for reasons which I only recently figured out). The problem of subtracting 8 from 35 would be simplified as such;

35 - 8 = 20 + (15 - 8)

I never quite got why this made the problem "easier" to solve, until, looking back recently, I realized that I was supposed to have MEMORIZED "15 - 8 = 7!"

At the time, I simplified it to this, instead. 35 - 8 = 30 + (5 - 8) = 20 + 10 + (-3) = 27, or, after some improvement, 35 - 8 = 30 - (8 - 5) = 30 - 3 = 20 + 10 - 3 = 27.

Evidently, I was happier using negative numbers than I was memorizing the part of the subtraction table where I need to subtract one digit numbers from two digit numbers.

I hated memorization.

Comment author: PetjaY 04 September 2015 06:47:05PM *  1 point [-]

I have a similar way, which i find simpler:
9N=10N-N
That is, 9 * 8=10 * 8-8