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Tez

BIDMAS - A Mathematical Question

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Tez   

As some of you may be aware A is currently having home tutors coming in to teach him. The teacher teaching him Maths is a History teacher. Yesterday A wanted to know why he has been taught a number of different methods of doing the following sum which will each give him a different answer.

 

what is the answer to

 

3 + 2 x 4

 

Answer using BIDMAS 11 ( The order is which you do each part is brackets, indices, division & multiplication of equal standing, so where together do them as they come, addition and suntraction of equal standing)

 

Older teachers have told him that he must work from left to right unless there are brackets or indices present in which case you do these first . Using this method the answer is 20

 

So obviously A wanted to know why he was being taught contradictory methods and how could he be certain which method was correct.

 

He was told that BIDMAS was the correct method because the Government had determined that the existing method taught by older teachers was confusing.

 

Has anyone else heard of this and just who is correct?

I have googled and BIDMAS does seem to exist.

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clair   

My auntie who is in her seventies was a maths teacher to A- level. She teaches primary schools voluntarily now. When she helped my daughter the other week with this very scenario she told her that you always do the multiplication and division bits first then the add or subtraction. why I will never know but she is just a genius in teaching maths. She makes the kids understand things when the teachers have confused them by putting it into real life scenarios. hope it helps. :D

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ray   

I'm lucky (!?) enough to work with actuaries - all higher maths degrees and anoraks - and they've just told me the answer is 11. You always do the multplication/subtraction first.

 

ray

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Canopus   

Many centuries ago, an international treaty was written by mathematicians for mathematicians dictating the order of priority of operations in a calculation. The order of priority is colloquially known as BIDMAS and is the ONLY correct method of performing a calculation.

 

I don't know where this idea of working from left to right comes from but it is complete tosh. I was never taught this bizarre method at school and suspect that it was invented by an English teacher because sentences are read from left to right.

 

3 + 2 x 4 = 11

 

(3 + 2) x 4 = 20

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Tez   

Callme jaded,

 

You've just reminded me, we did smp maths as well as it was definitely left to right, but that was before calculators and spreadsheets.

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Canopus   
You've just reminded me, we did smp maths as well as it was definitely left to right, but that was before calculators and spreadsheets.

 

I can't understand this. There is only ONE correct way to do a calculation and that is BIDMAS. This has been the case for over 1000 years and is considered sacrosanct by mathematicians.

 

A friend did the SMP A Level during the late 1970s and learnt things like matrices, set theory, group theory, and other "modern maths" topics rather than the usual algebra, calculus, and trigonometry that I endured. He never mentioned having to perform calculations from left to right but I will ask him about this.

 

Did any maths books ever say perform calculations from left to right?

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supersec   

am totally at a loss on this one! I must be the most uneducated person in the whole of the world! :blink:

 

To me the answer is 20 but then I never did anything other than CSE Maths! Oh well! :lol:

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Tez   

Canopus I don't know about when Call me jaded did her smp maths but at the school I attended all the books were hand made so I didn't actually see any text books so I can't answer that. What I can say is that brackets were used almost all the time to indicate the order in which you should do the calculation so it would have been unusual to see the sum set out as

 

3 + 2 x 4

 

It would either have been shown as

 

(3 + 2) x 4

or

 

4(3 + 2)

 

or

 

3 + (2 x 4)

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I obviously went to a posh school because we had textbooks.

 

I have a very vague recollection of the conventions changing when I did some BASIC computer programming in the dark ages when everything came out on green music paper.

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Canopus   

I can assure you that BASIC - despite all its faults and deficiencies - complies with BIDMAS.

 

Until I see a textbook that states that calculations are performed from left to right, I will conclude that some people have been taught by very bad maths teachers who don't understand their subject.

 

For many years I have been saying that the lunatics are running the asylum in Britain. I know teachers make mistakes, but for two independent people to be taught the same incorrect technique about performing calculations is almost beyond belief. Some teachers really need to go back to school.

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Tez   

Canopus,

 

This discussion has come about because A has had conflicting teaching in school. I have been through his Maths books and work that he has done correctly using BIDMAS has been marked wrong on numerous occasions, so the mistakes are still happening.

 

You are quite right BIDMAS is the correct way to do it and always has been during the period whilst A has been at school, so the confusion he has been caused is inexcusable, especially since he is on the Gifted Register for Mathematics and so obviously has a natutral ability.

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Canopus   

It disgusts me when teachers mark things wrong when they are right. Conflicting teaching is one thing. Teaching something that is blatantly untrue is another.

 

I suggest you send a letter to the head about this naming the guilty teachers.

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baddad   

DOH!!

 

It took me forty years to learn how to do it left to right!

(And, honestly Canopus, that WAS the 'usual' way of doing basic math all those years ago, no matter how archaic it seems to you young whipper-snappers or high achievers!)

All I will say is that Ben better not come to me for any help with his maths homework!

 

In actual fact, I'm just going to IGNORE all this BIDMAS insanity, and i'm just going to stick my fingers in my ears and go Lalalalala until the rest of the world does too...

 

La la la la la la la la la la ......................................................

 

(I get the feeling i may be here some time)

Happy bidmas, one and all ;)

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lancelot   

Oh god, maths equations...

I have to edit the damn things in textbooks sometimes, and i irritate the h*ll out of the authors by bunging in plenty of brackets to remove the ambiguity.

 

Then there's the lovely continental habit of using commas instead of decimal points... oh, just don't get me started!

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I can assure you that BASIC - despite all its faults and deficiencies - complies with BIDMAS.

 

Yes I know it does. I had to change the way I was programming to get the right answers. I am surmising that is why the NC (and I was educated pre NC) uses it.

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Tez   
Yes I know it does. I had to change the way I was programming to get the right answers. I am surmising that is why the NC (and I was educated pre NC) uses it.

 

The explanation given to A for the change was exactly this, the confusion caused with computer programming. Hence "old people" like me were taught left to right unless there are brackets, younger people were taught BIDMAS. A googled on the subject and found answers that say the same as Canopus that the order was established back in the 1600s and other answers that say that until the development of computers it was as it comes unless brackets tell you otherwise.

 

I rather like baddad's solution to the problem.....made me smile anyway. :lol:

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am totally at a loss on this one! I must be the most uneducated person in the whole of the world! :blink:

 

To me the answer is 20 but then I never did anything other than CSE Maths! Oh well! :lol:

Everything is spot on with me too! LOL. I did CSE Maths too and came away with an F! Guess that's why my answer to the question was '20' eh!! :lol:

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Canopus   

I predate the NC and have only ever been taught BIDMAS at school. I had maths teachers do things in strange ways or were difficult accepting alternative solutions to problems - read my article on fractions - but I was never taught anything in maths that was incorrect or untrue. I can vaguely recall some kids who performed calculations from left to right but were told it was the wrong method. Every maths book I have encountered employed BIDMAS and I have never seen a maths book that states that calculations are performed from left to right.

 

That explanation about computer programming is also wrong. High level languages were developed to comply with the ESTABLISHED laws of maths including BIDMAS. In fact it would be easier to produce a compiler or interpreter if calculations were executed from left to right because computers are designed to process data sequentially.

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I changed school 4 times in 5 years due to my dad being in the RAF and it used to annoy me no end that whenever I ended up in a school they seemed to work things out differently. I learnt the BIDMAS way, only to be told I was wrong at the next school and promptly dropped to the bottom set. Finally manage to climb my way back up, change school find they used BIDMAS and back to the bottom I'd go :angry:

 

Wonder if it's more to do teaching training assuming that primary teachers can do basic maths?

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Canopus   

Primary school teachers can't be experts at everything and many aren't experts at maths. I suspect that before the days of the NC, SATS, league tables, and inspections every week, primary teachers could get away with their errors more easily than today. If the school relied more on teachers to provide information rather than textbooks then a teacher that got something wrong could quite easily end up brainwashing the entire class!

 

Secondary school teachers are usually more knowledgeable in their subject than primary school teachers. Therefore they are less likely to inadvertantly brainwash kids.

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tinminer   

Surely, it is just sheer laziness to miss the brackets out - BIDMAS was obviously designed by someone who does NOT have Asperger Syndrome!

 

Adding the brackets gives total clarity, and avoids any confusion.

 

 

Why don't non-autistic people say what they mean!

 

PS, I'm 41, but only found out today that when people say on the 'phone after they have rung you, ''I'll let you go now....'', it means that THEY want to finish the conversation. And I thought they were being polite, as they had interrupted me!

 

People are strange!

Edited by tinminer

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Zemanski   

Primary school teachers have had to have GCSE level Maths since the 70s, I remember my Mum talking about it when she was thinking about teacher training because she struggled to pass hers in school.

 

These days all new teachers must also do a 'maths audit' as part of their training on top of the GCSE. I did it about 6 years ago when I was doing a post-graduate course, just after it was introduced. It's much more about the theory of Maths and the ability to explain concepts rather than just do them, quite tricky in places, and it definitely covers BIDMAS

 

Also the numeracy strategy units (daily lesson plans), which are now used by most schools instead of textbooks (they're pretty good actually although some of the methods may not be familiar to people who left school more that 5 years ago and are available to download from the standards site/ QCA site), use BIDMAS.

 

Zemanski

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tinminer   

The point is, faced with that sum in the REAL world, you would not know if the person who wrote it was using BIDMAS or not.

 

It could be a VERY costly accounting error - dimensions to a house extension, interest calculation, mortgage payments, etc etc.

 

I thought that school should prepare you for the real world, and not just more academia.

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We were taught to work from left to right (am ancient !) I also remember teaching this method using SMP maths on teacher training for primary age.

That said, I don't remember, ever, the brackets not being there ;)

Tinminer's point is a good one, imagine assuming someone had used BIDMAS where they hadn't ? I'm beginning to think my mortgage company don't when calculating how much the monthly payment is :sick:

 

wac

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Canopus   
Primary school teachers have had to have GCSE level Maths since the 70s, I remember my Mum talking about it when she was thinking about teacher training because she struggled to pass hers in school.

 

GCSEs didn't exist until 1988. Was it possible to become a primary teacher in the 70s with a grade 5 CSE or was a good grade at O Level required?

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Hi,

You needed a pass at GCE level in maths and english, ie. at least a 'c', in the early 80's, not sure about before then, those were there days when you didn't need a degree to teach, and I was just a pupil ...

 

 

wac

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Canopus   

Come to think of it. I reckon it would be possible to get a C at O Level if one calculated from left to right rather than used BIDMAS. O Level papers had questions on things like algebra, geometry, trigonometry, and calculus that don't require knowing the priority of arithmetic operators.

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Kathryn   

Don't know about Maths but I'm appalled at the number of primary and infant teachers who lack the basics of spelling, punctuation and grammar. This to me is far more important than knowing BIDMAS.

 

Having chucked the cat among the pigeons I'll just wish you a "HAPPY BIDMAS" and retreat. ;)

Edited by Kathryn

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