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(26 Posts)
redskyatnight Fri 07-Feb-14 08:29:15

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).

Quejica Fri 07-Feb-14 08:30:27


kelda Fri 07-Feb-14 08:32:22


noblegiraffe Fri 07-Feb-14 08:32:46

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

bruffin Fri 07-Feb-14 08:33:38


LIZS Fri 07-Feb-14 08:34:20

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

Quejica Fri 07-Feb-14 08:35:52

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

TheGreatHunt Fri 07-Feb-14 08:36:03

70. There's only one way to answer this one.

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

NotQuiteCockney Fri 07-Feb-14 08:38:22

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 Fri 07-Feb-14 08:41:18

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!!

bruffin Fri 07-Feb-14 08:41:47

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

2beornot Fri 07-Feb-14 08:42:09

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 Fri 07-Feb-14 08:42:31

Here is a link to a nice quiz for you all

bruffin Fri 07-Feb-14 08:42:59

cross posted

I would direct her to a bodmus calculator on line.

2beornot Fri 07-Feb-14 08:43:14

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

TheGreatHunt Fri 07-Feb-14 08:43:34



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

<is that right? blush>

Quejica Fri 07-Feb-14 08:43:59

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

Quejica Fri 07-Feb-14 08:46:26

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

TheGreatHunt Fri 07-Feb-14 08:49:55

<boasts> All correct in that quiz!

RunAwayHome Fri 07-Feb-14 09:34:56

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 Fri 07-Feb-14 09:40:23

Message withdrawn at poster's request.

prh47bridge Fri 07-Feb-14 09:51:50

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 Fri 07-Feb-14 09:58:54

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.

TheWomanTheyCallJayne Fri 07-Feb-14 10:00:03

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 Fri 07-Feb-14 10:00:57

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

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