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[Ohne Mitleid]

The nines multiplication table trick is kind of a fun thing to have in your repertoire, keeping in mind that it is usually most handy when you are dealing with youth who are just learning the more difficult aspects of math, mainly multiplication and division. You set up your pupil with a particular counting order for their fingers. It is usually easiest to do this with your fingers facing towards you, but either way, the counting order is one to 10 (ten actually ends up being zero, as you will see in practice) from left to right. Pick a number from one to 9 as the multiplier then count off that many fingers from the left to right. When you have arrived at your number, keep that finger held down. The number of fingers to the left of the held down finger will be the digit for the 10s spot and the number of fingers to the right of the held down finger will be the digit for the 1s or single digit spot. In the diagram attached, the example was for 3 times 9 which, if applying the rules above, automatically yields 27. I thought it was pretty cool, but cool would be a normal response from a geekwad and I am just a freakpod. At least they rhyme.

Things still work when you get to the tenth finger, which represents zero, which can be considered "special". Zero counts as zero, so the fingers to the left of it are 9 for the 10s place and 0 for the single digit yielding 90 (9 x 10). I usually try to further the whole process by taking it one more step. The next round beyond the one through ten phase is for 11 through 20, which is the result of the nines (1-10) finger trick plus 90. This incorporates addition and multiplication which usually deepens the understanding to the pupil that multiplication is really just the memorization of addition set results strung together.

Anyway, Have fun
Ohne

[_r.u.s.s.]

it seems to be fun to play with, but i'd rather teach my "pupils" how to do nines multiplication quickly and properly memorize it in their head

[DarthHelmet86]

I always was taught and use the 10s method, if you will.

It is simple. You times the number by 10, then subtract one of itself from the result. I.e,

65x10=650-65=585

9x65=585

[Ohne Mitleid]

I just thought it was neat, probably because I still value the moments of clarity when my memory can travel back that far!

I saw a program on some public network showing off the "new math". It pitted a kid with his brain and no additional tools vs. a kid with a calculator. The brain won every time. I adopted the method and had to unlearn (if you will) the old way. It's faster and easier for me.

You just do a reversal of the classic multiplication method and start multiplying on the left, instead of the right, and then add the totals. So for 9 x 65, your head would store 9 times six(ty) and then add 45. It doesn't sound better when you look at it, but once you have it patterned in your brain, it goes faster, IMO.

So why am I advertising something else, I wonder.

[Japo]

I'll go for a good old digital calculator every time, but

[_r.u.s.s.]

man, i remember that vid. it's impressive in a "wtf" sense but i'm pretty sure that doing

 21 x
 13
----
 63+
210
----
273

is like milion times faster

[Ohne Mitleid]

Originally Posted by _r.u.s.s.

man, i remember that vid. it's impressive in a "wtf" sense but i'm pretty sure that doing

 21 x
 13
----
 63+
210
----
273

is like milion times faster

It's like a paper abacus. I agree with r.u.s.s.! Wtf was the first thing that sped through my mind. Ok, and there it goes again... Wtf!?

[Japo]

Originally Posted by _r.u.s.s.

man, i remember that vid. it's impressive in a "wtf" sense but i'm pretty sure that doing ... is like milion times faster

Well with two-digit figures, sure. But the method in the video seems to be faster as the number of digits goes up.

But as I said, digital calculators FTW, of course that doesn't mean you shouldn't learn to calculate mentally, to a point, but training to beat a calculator, even if possible, is pointless. Cultivating mental skills in one thing, trying to deny progress that's decades old is another.

[Ohne Mitleid]

I think maybe what I was trying to get at was the loss of things that aren't really necessary skills, but passed over because some new electronic thing has since replaced them. Kind of an "I remember when.." moment.

This was all spurred on when I asked my friend what my phone number was. He immediately went to look at his cell phone and I told him to tell me what it was without looking. He had no idea. Without his phone, he was lost, at least regarding my number.

I don't want to tell you the resulting answer for the 'Okay then... And what's my last name?' question...

[_r.u.s.s.]

man, i don't know a single of my friend's phone numbers without reading it somewhere neither

it's easy to remember 3 or 4 numbers if you call a static line within the same town, because all the rest of the numbers are the same for the whole rest of the city. it's kind of more difficult to remember everyone's 6-10 digit cellphone number