Memorizing the 99x99 multiplication table

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#1 16 May, 2017 - 10:46
Joined: 10 months 1 week ago

Memorizing the 99x99 multiplication table


Curious to see how you guys would go about this. I think "linking" would be easy for the square numbers (44x44 = 1936 I'd probably link my pre-existing two-digit PAO + a major system object), but that won't work for any other combination. It's about 10,000 3- or 4-digit numbers to memorize.

Any ideas?

16 May, 2017 - 11:15
Joined: 2 years 8 months ago

I wouldnt want to suggest anything at the moment, but I will think about it. What I do know, is that you won't have to memorize 10,000 numbers.

of the entire 99*99 grid, you do have 9801 results, that part is true. But here is the trick:
99 of those are square numbers, leaving those out for a second.
that means you got 9702 non-square results. but when you look at it, it has both 45*82 and 82*45, which are exactly the same. Meaning you could leave a lot of those out.
In fact, you can leave 4851 numbers out, leaving 4851 numbers to memorize. Plus the 99 squares, that makes for 4950 numbers.

16 May, 2017 - 11:28
Joined: 10 months 1 week ago

Great point! Looking forward to what you come up with :)

18 May, 2017 - 10:11
Joined: 1 year 7 months ago

Actually you don't need memorized that squares you can do it mentally very fast with practice just do this;

That means:

1. Round up or down to the nearest multiply of 10. (In the previuos example round down to 40 subtracting 1)
2. Add the same distance from the nearest 10 multiply to the original number (In the previous example add 1 to 41 and get 42)
3. Multiply the two number you get, don't worry that multiplication is easy in all cases (In the previous example multiply 42 by 4 and attach a 0... 42x4 = 168.. then attach a 0 and you get 1680)
4. Add the square of the distance you got in the previous steps. (It will a small number allways )

I know it seen complicated the first time but this method is very very fast believe me.. Look in google "Mentally square a two digit number" and you'll get a better explanation of this method, maybe you get confused because I don't know how to explain it more clearly and my english doesn't help hahaha

18 May, 2017 - 13:23
Joined: 10 months 1 week ago

Yeah! I'm reading Secrets of Mental Math, so that's how I've been squaring numbers mentally, too!

The author has all the two-digit squares memorized (probably by rote). Which helps with calculating 3-digit squares (you skip having to square a two-digit number to calculate what to add in the end underlined as such: [431 x 431 = 400 x 462 + (31x31) ). So since you'll already know 31x31, you don't have to break that down into 31 x 32 + (1 x 2).

So with the same logic, I was wondering about memorizing the 99x99 table, so that doing 3-digit by 3-digit multiplication (and 4 x 4 etc) becomes way easier :)

24 May, 2017 - 22:55
Joined: 9 months 2 days ago

I agree, I started thinking like this when I first got into memory training, but with some experience now, I can wholeheartedly say...I would avoid the work of memorizing numbers that you can get by calculating them. Memorize the calculation method and practice that; your mind is already programmed to make calculations, it's much less work to just practice this skill as opposed to spending the same amount of time memorizing data without any relationship to 'how' you got there. Memory Palaces and the like are for memorizing things that you can't find with another method of brain usage. Like you don't need to memorize in a Palace the different forms of smells that different foods give you because you already have other senses available for this.
My two cents: use memory techniques for assembling unrelated (playing cards order, shopping lists, dates+facts) items that aren't memorable via other methods of brain function.

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