# Talk

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

(35 Posts)
withgreatpower Wed 09-Jan-13 21:49:58

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 ...

realcoalfire Thu 10-Jan-13 10:03:01

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

realcoalfire Thu 10-Jan-13 10:17:03

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'

changejustforyou Thu 10-Jan-13 10:26:26

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....

drjohnsonscat Thu 10-Jan-13 10:33:22

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.

mummytime Thu 10-Jan-13 10:38:43

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.

Houseworkprocrastinator Thu 10-Jan-13 10:43:54

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.

withgreatpower Thu 10-Jan-13 13:13:32

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!

trinity0097 Thu 10-Jan-13 20:53:38

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)

tinytalker Thu 10-Jan-13 21:36:15

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

cory Thu 10-Jan-13 22:12:27

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.

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