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Author Topic: a maths question  (Read 8392 times)

dougal99

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Re: a maths question
« Reply #25 on: May 24, 2011, 05:10:53 pm »

Tiger tiger

I'm relaxed all my children are grown up and my homework helping days are over. However, others with schoolkids are being taught the 'new' methods so they can help their children. If that teaching is flawed the help is a disadvantage not an advantage. Your law of diminishing errors does not work if the teaching at one level is flatly contradicted at a later level. It matters whether you do division or multiplication first so the rule must be consistent whether in primary school or at university. Any given calculation must have the same result whenever you perform it, otherwise mayhem!
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philk

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Re: a maths question
« Reply #26 on: May 24, 2011, 08:20:38 pm »

i the real world tho who the hell does a sum and multiplys by 0
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craftysod

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Re: a maths question
« Reply #27 on: May 24, 2011, 08:45:29 pm »

AHHHH !
My head is going to explode,just spent an hour or so going through,the maths coursework for my plumbing course.
Now remember i left school in 1979 and never could work out pie,volumes,masses and the rest of it.
Come on to see about boats,and see more maths  {-)
Mark
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meechingman

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Re: a maths question
« Reply #28 on: May 24, 2011, 09:34:40 pm »

i the real world tho who the hell does a sum and multiplys by 0
I'm sure that sum do!  :embarrassed:

Worse still are those that divide by 0!  {:-{
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tigertiger

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Re: a maths question
« Reply #29 on: May 25, 2011, 04:26:35 am »

Last year Martin gave us moderators a 10% pay rise.  :-))

0 x 110% = 0

He did, honestly.  :-)
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nick_75au

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Re: a maths question
« Reply #30 on: May 25, 2011, 04:40:42 am »

to make the answer 0 the equasion would have to be
(10 +10) x 0  = 0

Nick
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Trooper63

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Re: a maths question
« Reply #31 on: May 25, 2011, 06:52:28 am »

From what I was taught, the sequence to calculate numeracy is:

Brackets or Divide, Multiply, Add and Subtract (BODMAS)

therefore,
10 + 10 x 0
10 + (10 x 0)
10 + 0
10


As Kleban has said, BOMDAS is the world wide mathematical principle (was when I did school 60/70s).  IF there are no brackets, then do all the dividing and multipling, then and only then start adding and then subtracting.   It is a simple principle.  It does not follow english language principles of left to right.
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dougal99

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Re: a maths question
« Reply #32 on: May 25, 2011, 01:37:45 pm »

I was in school up until 1967 and BODMAS was definitely not taught to me. Unless there were brackets, you moved left to right. I suspect the advent of scientific calculators, and their use in schools caused the change. When I was in the sixth form we had a real 'monk on' when we found that the fourths were using slide rules!

Technology. Don't you just love it?
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JerryTodd

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Re: a MATH question
« Reply #33 on: May 25, 2011, 03:11:02 pm »

It's really quite disturbing to see so many not only do something so simple incorrectly, but clucking like chickens about "That's not how I was taught!"

The order of operations for solving math problems has been around longer than anyone on this forum's been on Earth - it's nothing new.

I imagine fellows like Camping went to the same schools, which is why he can't figure out the right date for the end of the world.
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tt1

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Re: a maths question
« Reply #34 on: May 26, 2011, 12:51:40 am »

Jeez!, aint half glad my life don't depend on any of this!  {-) {-) {-)
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Norseman

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Re: a maths question
« Reply #35 on: May 26, 2011, 09:15:22 pm »

Hey

I got as far as the end of TigerTigers post and I thought hey - I actually get it and give Tiger a prize! I read on, lost the will to live, and have opened the magic mead again - soon everything will make perfect sense again.

Regards Norseman
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omra85

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Re: a maths question
« Reply #36 on: May 26, 2011, 11:00:23 pm »

Its funny what you were taught at school.  I always loved English Language but cared little for the difference between a pronoun and a preposition.  They were terms to describe something I would be using, but I felt it was more important to concentrate on the meaning and use of the words.  This, and the correct use of punctuation, have been of more use to me throughout my life, than the fancy names given to words.

It was a similar situation with maths.  Ok, I have occasionally had the need to use some trigonometry, and possible even basic algebra, but a great deal of what I learned has been completely useless.  For example, I have never felt an overwhelming desire to find out the height of some landmark or other with the aid of a protractor.  I could look it up in Encylopedia Brittanica - or even easier nowadays, "Google" it!
As for quadratic equations ...

The modern generation may have the technological advantage over me, but when I see the level of basic education, I cringe!

Btw (see, I'm not a complete Luddite)  has anyone ever found a use for negative numbers?  I certainly haven't, unless you include my 'shopping' costs when being relayed to my dearest!

Cheers
Danny


 
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Norseman

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Re: a maths question
« Reply #37 on: May 26, 2011, 11:38:13 pm »

Ok the magic mead is working now, things are getting clear

Negative numbers are everywhere from the balance sheet to the weather man to electronics. What is more mind blowing is some guy a few hundred years ago has some magic mead  and starts pondering the possibility of a square root of minus 1 - down in the shed where he can get out of the earshot. This gets forgotten/ rediscovered and we end up with the imaginary number i. Next thing you know the maths guys have engineers making sat navs and computing impossibley difficult stuff using i. Marvelous thing maths - I'm glad someone understands it.

Regards Norseman
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Spook

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Re: a maths question
« Reply #38 on: May 27, 2011, 12:37:36 am »

0 - either using a computer or using the noddle. No brackets means calculate from left to right and, as any fule kno, when you multiply anything by zero, the result is zero. i.e. 10 carrots + 10 carrots = 20 carrots, but 20 carrots times nothing is nothing. Simples *squeak*

Oh, and there is no such thing as minus numbers. I just drove 50 miles in my car and my petrol gauge dropped a few notches, so I drove back again, -50 miles, but my petrol tank didn't fill itself up again. I'd like 10 carrots please - why can't you give me -10 carrots? Because you're not  mathematician and this is an underrtakers? Ok thanks very much, I'll go and see if the doctor can help. NUUUURSE. the screens , please!
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Trooper63

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Re: a maths question
« Reply #39 on: May 27, 2011, 04:36:40 am »

I'll put a sheep station on it......................  :embarrassed:
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nick_75au

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Re: a maths question
« Reply #40 on: May 27, 2011, 07:33:29 am »

Multiply or Divide before you Add or Subtract. Example:
yes         2 + 5 3    =    2 + 15    =    17
   
no         2 + 5 3    =    7 3    =    21 (wrong)

Its exactlythe same equation <*<

Straight from the link I posted >>:-(

Nick
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derekwarner

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Re: a maths question
« Reply #41 on: May 27, 2011, 07:40:31 am »

 :(( {:-{ mmmm

Some time ago I was listening to my eldest daughters partner [university graduate] talking about negative equity    <:( now I had studied a little economics @ the University of Wollongong light years ago.....but did not recall this term when associated with a motor vehicle

How silly could I be  {-)...it simply means he owes more money $ in continued lease repayments that the vehicle is worth

So does this constitute a negative number? ........Derek

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knoby

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Re: a maths question
« Reply #42 on: May 27, 2011, 06:29:48 pm »

At high school I was taught 10 + 10 x 0 = 0
Then I went to further education & was taught 10 + 10 x 0 =10
After further education I wen to the university of life & that taught me that life's to short to worry about it   %%

cheers Glenn
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tigertiger

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Re: a maths question
« Reply #43 on: May 28, 2011, 12:37:57 pm »

:(( {:-{ mmmm

Some time ago I was listening to my eldest daughters partner [university graduate] talking about negative equity    <:( now I had studied a little economics @ the University of Wollongong light years ago.....but did not recall this term when associated with a motor vehicle

How silly could I be  {-)...it simply means he owes more money $ in continued lease repayments that the vehicle is worth

So does this constitute a negative number? ........Derek



It is not a negative number.

If you default someone will come after you for the balance, I am positive about that.

 %) %)
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RaaArtyGunner

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Re: a maths question
« Reply #44 on: May 28, 2011, 12:42:11 pm »

Just wondering that with all the positves and negatives whether this question should be moved to Electrical, batteries etc

 %) %) %) {-) {-) {-)
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tigertiger

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Re: a maths question
« Reply #45 on: May 28, 2011, 12:56:57 pm »

Ah!
That reminds me of another one of those rules of diminishing errors.

In middle school physics, up to grade 10, we were taught basic circuits. We were told that electricity flows from positive to negative, and used this assumption in circuit diagrams.

However, in high school (grade 11-12) we were told that actually electricity is the flow of electrons. Therefore the flow of electicity is from the negative terminal towards the positive (in a DC circuit).
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PMK

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Re: a maths question
« Reply #46 on: May 28, 2011, 02:30:58 pm »

Very impressive, Tiger! You obviously know your beans. There you are, giving the impression that you're just a humble model boat builder, yet you're actually a living, breathing mine of information.
Back in the days of Mssrs Ohm, Faraday, Hertz, et al, it was widely accepted that the direction of current flow was always emitted from the Anode (positive) terminal and to end up at the Cathode (negative) terminal. That was the convention of the day, hence the phrase "conventional current flow" was coined. Of course, we now know that the opposite is true, that electron current actually flows from negative to positive - otherwise called "electron current flow". An example of proof can be seen when we suffer that so-called dreaded "black wire" syndrome on our R/C battery connections.
Oddly enough, and quirky as we humans are, we still quaintly refer to current flow in the conventional sense.

And so end'eth today's history lesson #257b.
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roycv

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Re: a maths question
« Reply #47 on: May 28, 2011, 03:05:35 pm »

Hi PMK, I did not know that electron flow was the reason for the black wire problem.  I have just been changing plugs on a servo and have a wire gone black all the way down about 4 inches of it. 
Are all negative wires on our RC destined to go this way?

I have been using RC since 1957 and have only found a few wires in this condition.  I would appreciate a technical reason for it, or better still a solution.
regards Roy
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Welsh_Druid

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Re: a maths question
« Reply #48 on: May 28, 2011, 04:36:04 pm »

. Of course, we now know that the opposite is true, that electron current actually flows from negative to positive - otherwise called "electron current flow". And so end'eth today's history lesson #257b.

I don't doubt this for a minute - but why then are we told to put a fuse between the POSITIVE battery terminal and a motor ?

Don B
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PMK

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Re: a maths question
« Reply #49 on: May 28, 2011, 05:16:01 pm »

Don: Because it harps back to those days when conventional current was considered the done deal. The positive (Anode) is still considered the so-called "hot" connection (even more so in AC circuits), so fuses by convention are placed in series with the positive rail. Also, bear in mind that in most modern circuits the negative is mostly always tied to ground in one way or another. The negative connection of, say, your R/C reciever will also be tied to the negative, of, say, your servos... and your ESC and your LEDs, etc. So it makes sense to fuse the positive side only.
Incidentally, most folk, when measuring the current in their circuits, will mostly always connect their ammeter in series with the positive rail. Did you know that you will get a much truer reading of the total current draw if the ammeter is connected in series with the negative rail? A thousand Green Shield stamps to you if you can tell me the reason why.

Roy: Black wire syndrom is basically a chemical reaction of the negative copper wire coming into contact with air. It's even more noticable when the air itself is humid or damp - a form of electrolyosis, very similar to how tin plating works. Try placing a copper probe and a zinc or stainless steel probe in a solution of acidic/salt water, then connect both probes to a DC supply. After a while you will begin to see the aforementioned chemical reaction taking place in the form of bubbles collecting around the probe which is connected to the supply negative probe - not the positive probe.
The general advice for R/C modellers is to not store their models in a cold, damp shed. If you must store your models in a damp environment, then a simple prevention of black wire syndrome is to disconnect the battery/batteries altogether. Better still, it's recommended to remove the batteries from the model during the Winter months and keep them in a room at normal ambient temperature.

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