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Join our Primary Education forum to discuss starting school and helping your child get the most out of it.

Join our Primary Education forum to discuss starting school and helping your child get the most out of it.

Primary education

BODMAS

25 replies

redskyatnight · 07/02/2014 08:29

DS is learning about BODMAS at school.

What is the answer to the following problem?
60 - 4 + 9 + 5 =

(I disagree with his teacher and am a maths graduate so obviously think I am right, but quite prepared to be told I have forgotten basic mathematical concepts after not doing any maths for years).

OP posts:

Report

Quejica · 07/02/2014 08:30

70

kelda · 07/02/2014 08:32

70

noblegiraffe · 07/02/2014 08:32

70, work from left to right when there is no priority.

bruffin · 07/02/2014 08:33

70

LIZS · 07/02/2014 08:34

70 - it's not a B(I)ODMAS problem thought.

Quejica · 07/02/2014 08:35

Yes, they do call it BIDMAS now which actually makes more sense than BODMAS.

TheGreatHunt · 07/02/2014 08:36

There's only one way to answer this one.

Did you mean to put multiply or divide in there!?

NotQuiteCockney · 07/02/2014 08:38

I think if you just learn BODMAS, and don't learn that addition and subtraction are at the same level then you might come up with a different answer.

But yes, 70 is the answer. Wikipedia agrees - look in the Mnemonics section.

redskyatnight · 07/02/2014 08:41

It was on a sheet of BODMAS problems he had for homework - DS was struggling so I went through them all with him very slowly (there were obviously other questions that included brackets, multiplication, division).

We got "stuck" on this question as DS (who likes to follow rules) insisted that Addition came before Subtraction despite my giving him a really boring over his head mathematical explanation why not. Anyway he eventually submitted the homework with the answer 70 (still not happy) and is now disgusted with me because his teacher is insisting the answer is 42 (and he missed out on a merit point).

So next question is - assuming this story has not got garbled in translation, what on earth do I do about it? Don't want to march into school and accuse the teacher of teaching Y5 dodgy maths!!

OP posts:

bruffin · 07/02/2014 08:41

I suspect the teacher has come up with 42. Somehow making it
60- (4+9+5)

2beornot · 07/02/2014 08:42

I can see how it could be easily misunderstood and calculated as 60 - (4+9+5) but that's wrong!!

Answer is def 70

Quejica · 07/02/2014 08:42

Here is a link to a nice quiz for you all

bruffin · 07/02/2014 08:42

cross posted

I would direct her to a bodmus calculator on line.

2beornot · 07/02/2014 08:43

I'd tell her she was wrong. It's not fair on your ds plus it's wrong!!

TheGreatHunt · 07/02/2014 08:43

42?!!!

Ridiculous.

I remember it that when you have problems with + and -, the - "sticks" to the number to its right. you cannot seperate them with brackets.

Quejica · 07/02/2014 08:43

You absolutely go to the school and make a fuss - and get your son his merit mark!

Quejica · 07/02/2014 08:46

With + and - the rule is that you just work from left to right.

TheGreatHunt · 07/02/2014 08:49

All correct in that quiz!

RunAwayHome · 07/02/2014 09:34

Easiest to think of addition and subtraction being the same, because the sign has to stay with the number, so it's a -4, and then you can do them in any order you like to make the calculation easier. Personally I did the 9+5 and then the -4 because I could see it made 10 and then added that on, to get 70.

42 is definitely wrong, if there are no brackets.

TravelinColour · 07/02/2014 09:40

This reply has been deleted

Message withdrawn at poster's request.

prh47bridge · 07/02/2014 09:51

As others have said the teacher is definitely wrong. The answer is 70. BODMAS does NOT mean you do addition before subtraction (nor does it mean you do division before multiplication). Strictly it is:

B O (or I) DM AS

The teacher has taught the class incorrectly. It needs to be fixed as soon as possible otherwise it will cause problems for the pupils later.

Point the teacher at the Maths is Fun website. That gets it right. If the teacher continues to insist the answer is 42 refer the matter to the head. If the teacher is getting it wrong they need to be corrected.

noblegiraffe · 07/02/2014 09:58

Secondary maths teacher, please tell her she is teaching BIDMAS wrong.

It's brackets then indices then
division AND multiplication, then
Addition AND subtraction

She obviously thinks it's a strict order and she needs to be told.

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TheWomanTheyCallJayne · 07/02/2014 10:00

Please tell the teacher they're wrong
You only have to look on mn to see how many people don't understand bo-dm-as (or don't know of it at all). Let's try and have a generation who grasp it.

TheWomanTheyCallJayne · 07/02/2014 10:00

Bloody autocorrect. b o-dm-as was what I put

craftynclothy · 07/02/2014 14:39

Please tell her she's wrong. There might (will?) be parents who don't know that she's wrong or who are confused by her explanation.

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