## when the teacher is wrong, and a bit arrogant...

(35 Posts)Today my DD's teacher (Year 6) lost her patience with DD.

The pupils were given a question like: "Work out 2+3x5 ". The teacher said that you have to put brackets like this: " 2+(3x5) " otherwise the question doesn't make sense. My DD said (correctly!!) that you don't need brackets, as you have to do multiplication before addition anyway. The teacher insisted, DD insisted, teacher snapped and said something like "I did A level Maths, so I know what I'm talking about".

DD stopped trying to explain...

DD was a bit sad at this (she very rarely/never gets teachers cross). We (DD and I) talked about this, and I used it as a lesson to learn:

1) just because somebody is a teacher, doesn't mean they don't make mistakes

2) it's just a mistake, everybody makes mistakes

3) when you don't think something is right, go check in other ways, don't just trust one source of information

I also added that maybe the teacher was tired, and was having a bad day, so she lost her patience. DD asked "So this teacher is always tired?" (teacher doesn't have much patience in general).

I just wanted to share this story - I'm not too bothered by the mistake, but I keep telling my children that, if something the teacher says doesn't seem right, they should double check by asking other teachers or by looking in Maths books etc (I'm talking about myths like you cannot do "4 minus 6" -- of course you can! you get a negative number, but you can do it!; or that the answer to 6 divided by zero is zero -- AAAAAAAAHHH No it's not zero, it's infinity)

Sorry, not a very interesting post, but I just wanted to share ...

When I was a child I always thought it was the teachers who couldn't admit they were wrong who came across as really insecure and lacking in authority. When a teacher was relaxed enough to occasionally admit limits to his knowledge, I tended to assume that he probably knew rather a lot... A lifetime in education has confirmed this hunch.

It's like children don't necessarily trust the authority of the teachers (or parents) who shout and rant and dish out punishments all the time: even very young children are savvy enough to suspect that is a sign of weakness.

Thank God I teach pre-prep is all I can say

The I in BIDMAS stands for indices, however the O in BODMAS was never clear as to what it stood for (e.g. Over, of are just two examples I heard as a child)

**realcoalfire**, thanks for that! You are right! It's not correct to say that 6/0 is infinity. Division is not defined if the number you are dividing by is zero.

It's true that 1/x (or 6/x) approaches infinity as x decreases to near zero, but if x ever exactly gets to equal zero, the answer becomes undefined.

(I looked it up here, by the way www.newton.dep.anl.gov/askasci/math99/math99259.htm (post by Bob Avakian ).

Well, it's good to learn something!

BIDMAS? what happened to BODMAS?

Think i might be so out of date with math. Is it possible the teacher was explaining what goes first and was asking the class to put the brackets in to make sense of it?

Teachers are only human though and do make mistakes. my daughter was told in school that a word she said was not a real word. We looked it up together... it is in the oxford dictionary and originates from the 17th century. I did tell her people make mistakes and not to go in the next day and tell her she was wrong.

drjohnsonscat you have translated it into a number sentence, however as written the rule is Brackets Indices Division Multiplication Addition Subtraction, if you want to do the addition first you do **need** brackets. It is often a good idea to make sure you use brackets to make sure there are no mistakes.

6 divided by 0 can be anything between 0 and + or - infinity; or so I was told at A'lvevel.

I don't know what bidmas means but surely whether you do the multiplication first depends upon what the sentence is supposed to mean.

If you mean that three children had five sweets each and then their mother gave them another two then you do the multiplication first.

If you mean that one girl had two cakes and one girl had three cakes and they decided to pool their cakes and then cut each cake into five to share it among the class so how many slices do you end up with then you can do the adding first.

ha realcoalfile, was just thinking about that "infinity" stuff. That's what I used to think. Whilst revising with dd for her entrance exam I read about it in wikipedia. I didn't really understand it, but realised that I was wrong in saying infinity....

**OP wrote** the answer to 6 divided by zero is zero -- AAAAAAAAHHH No it's not zero, it's infinity)

That is wrong .6/0 is undefined not infinity.

Undefined means that it is not possible (unsolvable), while infinity just means without end or 'unboundedness'

You don't need brackets obviously, but perhaps the teacher was just telling them to put brackets in as a technique, to make it look clearer and less likely they will make a mistake

I teach teenagers and I am not afraid to say, 'I don't know' or ,'are you sure? Let's check that'.

All teachers should IMHO.

<not very useful>

Isn't the teacher just putting brackets in as a reminder that you do the multiplication first? To break the sum down?

It doesnt need brackets. BIDMAS means you work through each in order if they are present. So if there is only addition and multiplication then you just need to remember to multiply first then add and not simply complete the sum as it is written.

Of course BIDMAS applies! If you want 25, that's when you need the brackets

See this is when I am glad I teach secondary - if you teach yr 6 the chances are that the brightest pupils will exceed your knowledge in some area (for me it would probably be science or maybe ICT!) and yet you still have to teach them!

This is not a problem in secondary thank goodness

OP I agree, your DD needs to learn that teachers are not always right (I sometimes can't answer a question but try to be honest) and also how to deal with that situation.

Out of interest, why would you think the BIDMAS rule wouldn't apply in this case?

**Amerryscot** I have to say that it really does NOT need brackets at all. BIDMAS applies in every calculation you ever see, so multiplication ALWAYS needs to be done before any addition or subtraction.

BIDMAS means you are never in doubt. You only *have to* use brackets where the normal rules don't apply.

Teachers are often wrong - they are human beings. We live in a culture which accepts human error and encourages polite, constructive correction.

Someone I know teaches maths in a British boarding school that has a lot of Malay/Chinese pupils. They **never** correct teachers. They will copy down 2+3=62 without a murmur. We wouldn't want our children to be *that* accepting of a teacher's authority.

On the other hand, some children challenge obnoxiously. I did this to our ~~utterly shit~~ A-Level German teacher, who was eventually so exasperated she sentenced me to teach the next lesson, on the subjunctive. It backfired on her though, as I did it, and taught her things she didn't know...

**Amerryscot**, I might be wrong... but I think my DD was right. Have a look at www.bbc.co.uk/bitesize/ks3/maths/number/order_operation/revision/2/.

However, I am ready to listen to your explanation.

**learnandsay**, I see your point. The teacher needs to have authority to be in charge.

However, and maybe it's not totally related, I remember reading that the majority of plane crashes happen when the more experienced, senior pilot is flying the plane, because the younger pilot (who might have understood there is a problem, and wants to tell the pilot how to avoid crashing) doesn't trust his knowledge enough to question the pilot's decisions. The authority of the senior pilot is actually dangerous in this case, as the younger pilot can't conceive that he himself is right, and not the experienced pilot. That's why I think this was a good lesson for my DD to learn, not so much for the teacher.

See I thought 2+3x5 was 25 whereas 2+(3x5) was 17.

Clearly not as good at maths as I thought.

And no, I'm not the teacher...

2+3x5 does really need brackets.

You can't just look at the expression and decide that the multiplication needs to be done first. The BIDMAS rule doesn't really apply in this situation.

I would have to say that in this example of pupil tattle tailing is that parents shouldn't believe everything that happens in school, and therefore teachers wouldn't believe everything that happens at home.

enjoying the idea of a clever nine year old on the news. But teachers are used to exposing themselves to ridicule and challenges from kids. It's par for the course and sometimes clever kids are right. Damn those clever kids

I think we're also talking about a situation where the teacher actually thought that she was right. It can be very difficult to persuade anyone that their cherished view is in fact wrong. And I'm guessing that it's even more difficult if the critic is eight years old. Why do we always have adult experts on news channels rather than clever nine year olds?

See - I made one there...

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