Re: Complacency

Here's another one, from the 1933 classic, Mathemagic. Of course it was
originally presented without the calculator:

Enter the number 12345679 onto a caluclator.
Ask someone to pick their favorite number 1-9 and tell you what it is
Silently times their number by 9, and enter, for example, X 54 (if
their number was 6)
Show them the resulting display of a long line of their favorite digit.

this works because 12345679 x 9 = 111111111, so if instead you multiply
by 9 times a digit, then you get a line of those digits, invariably
greeted by "how'd you do that??"

Another one involves the conversion of sevenths to decimals
1/7 = .142857142587..... Any other nubmer of sevents is the same
number starting with a different digit
2/7 = .285714285714...
3/7 = .428517428517...

and so on.

Morris


Alan S wrote:
On Mon, 17 Apr 2006 06:40:50 -0400, "Roger Zoul"
<rogerzoul2@xxxxxxxxxxx> wrote:

Chris Malcolm wrote:
:: Susan <nevermind@xxxxxxxxxx> wrote:
::: Roger Zoul wrote:
:::: bj wrote:
:::::: "Roger Zoul" <rogerzoul2@xxxxxxxxxxx> wrote in message
:::::: news:1243bose6mf9g6d@xxxxxxxxxxxxxxxxxxxxx
:::::::
::::::: If they can learn the multiplication tables,
:::::::
::::::
:::::: Those have gone out of fashion. Along with any kind of mental
:::::: arithmetic, no matter how simple, let alone memorization of
:::::: anything.
::::
:::: Why do you say that? My gf's 7-year old has been learning this
:::: tables. So if they are still taught, they aren't out of fashion.
:::: And just because it is easier to use a machine, it doesn't mean
:::: that people don't know multiplication.
::
::: It's just de-emphasized and not drilled into automatic recall the
::: way it was when we were young. With calculators encouraged during
::: test taking, it's not as critical. So while it's covered, I don't
::: know any publicly educated young people who've learned and
::: memorized timestables the way we did years ago.
::
:: And they don't always know how to use calculators either. I once
:: tried to buy three things in a backpacking shop which were on a 20%
:: sale discount. The computer based tills were down, so after my
:: assistant failed to do the arithmetic on paper he called for help.
:: Two other assistants fiddled away for a bit with the numbers and
:: were unable to get sensible answers, so they called in the manager.
:: The manager went off and brought back a calculator. But none of them
:: could work how to do percentage sums on the calculator. They
:: couldn't work out how to use the % key, or how to do 20% discount
:: without using a percent key.
::
:: I was the only person in the shop and I think all this took at least
:: fifteen minutes. None of them asked me to help. I think they assumed
:: that a very old man would have even less clue about arithmetic than
:: they had. They were in their late teens and early twenties and
:: probably thought I was nearly dead and buying stuff for my grandson.
::
:: In the end the manager took a management decision and gave me
:: everything for five pounds. The correct answer would have been nearly
:: three times that.
::

I'm not sure why you didn't just help them along, Chris. I'm sure they
would have appreciated your help and it would have taken less time. Since
you didn't offer any help, they likely figured you didn't know too (i doubt
it had anything to do with your age).

BTW, I don't think this means that our young folks can't do math in the US.
These are folks who work in some shop and they've gotten use to using
machines. Don't use it, you lose it.


Memory is a funny thing. I still remember some of the
"trick" rules from Primary School.

If the sum of the digits was divisible by three - the whole
number was; so 4572 -> 4+5+7+2=18, so it is divisible
without a remainder. But 4571 isn't.

If the last two digits were divisible by four, the whole
number was; so 2012 is, 2013 isn't. Useful for leap years
and Olympics:-)

To multiply a 2 digit number by 11, separate the two digits
with their sum, so 45x11 -> 4 (4+5) 5 -> 495.

To divide by 25; multiply by 4 and shift the decimal two to
the left.

Any digit divided by 9 was the digit repeated - except for 0
and 9. So 8/8 is .888888, 2/9 is .22222

There were others for 8s, 5s, 6s; 7 was the hard one.

Remember Trachtenberg? I was fascinated by him for a while,
but the calculator made his theory an idea which came too
late. Forgotten it all now.

I've more than once been in the situation where the computer
at the checkout is slow for just a few items, so I tell the
checkout operator the bill and the change due - but they
wait, and wait, then finally the result appears and they
look at me like I'm from Mars because the numbers were
right. All of you from my era can do that. We all did
"mental arithmetic" in Primary/Elementary School. But you
need to keep in practice; like working out your exact fuel
economy to a couple of decimal places after you fill the car
by dividing the quantity into the distance in your head.
Just takes practice, not nous.

Maybe I'm just strange:-)



Cheers, Alan, T2, Australia.
d&e, metformin 2x500mg
--
Everything in Moderation - Except Laughter.

.

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