Help with sum

11 Plus Maths – Preparation and Information

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Beckii330
Posts: 57
Joined: Tue May 29, 2012 9:16 pm

Help with sum

Post by Beckii330 »

Hi, can someone please tell me the answer to this sum:

5+-4x-3

I think it is 17 but my son thinks -2. I explained about BODMAS and went to show him on a calculator but it also came up with -2 :? .

Thanks!
Tagore
Posts: 121
Joined: Thu Jun 14, 2012 10:28 am

Re: Help with sum

Post by Tagore »

Hi Beckii330

I believe they are required to work from left to right at this stage. I have no explanation for 'why'.

My answer comes out as follows, working from left to right in stages :

5 + -4 = 1
1 x -3 = -3

If you apply the BIDMAS or BODMAS rules then I concur with your answer of 17.

Hope someone can verify this.
Tagore
daveg
Posts: 247
Joined: Thu May 10, 2012 9:30 am

Re: Help with sum

Post by daveg »

Tagore wrote:Hi Beckii330

I believe they are required to work from left to right at this stage. I have no explanation for 'why'.
I'd be surprised if a question involved knowledge of negative numbers but insisted on pupils using the wrong method to obtain the wrong answer.
Amber
Posts: 8058
Joined: Thu Sep 24, 2009 11:59 am

Re: Help with sum

Post by Amber »

Where has this question come from? Surely it needs some brackets to be answerable? And is it really an 11+ question? Ugh.
Cozen
Posts: 19
Joined: Sat Jun 23, 2012 12:45 am

Re: Help with sum

Post by Cozen »

I believe that at 11 plus level, you are required to apply BODMAS/BIDMAS.

So -4x-3 =12
12+5=17

Using a calculator gives you 17 as well.
yoyo123
Posts: 8099
Joined: Mon Jun 18, 2007 3:32 pm
Location: East Kent

Re: Help with sum

Post by yoyo123 »

The papers set by GL assessment do not require Bodmas, you work from left to right.

Where was this question from Beckii330?
Tagore
Posts: 121
Joined: Thu Jun 14, 2012 10:28 am

Re: Help with sum

Post by Tagore »

Hi daveg
Cannot agree with you more. However, if you look at the questions they are normally set, they do not require the knowledge of BIDMAS. Even if BIDMAS were applied, the answer always comes to the same as when working form left to right. In this case, I am afraid, it is a rogue question. Neverthelss, it would be useful if someone would verify the my "11+" method.
Tagore
Beckii330
Posts: 57
Joined: Tue May 29, 2012 9:16 pm

Re: Help with sum

Post by Beckii330 »

Hi and thanks, it was just from a sample entrance paper for Year 7 at an independent school - hence no answers.

That's good to know about GL papers not requiring BODMAS - I am a novice at this 11+ stuff and so am fumbling about in the dark.
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