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 Post subject: Help with sum
PostPosted: Sat Aug 25, 2012 10:01 am 
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Joined: Tue May 29, 2012 8:16 pm
Posts: 57
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!


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 Post subject: Re: Help with sum
PostPosted: Sat Aug 25, 2012 10:46 am 
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Joined: Thu Jun 14, 2012 9:28 am
Posts: 121
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


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 Post subject: Re: Help with sum
PostPosted: Sat Aug 25, 2012 11:06 am 
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Joined: Thu May 10, 2012 8:30 am
Posts: 247
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.


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 Post subject: Re: Help with sum
PostPosted: Sat Aug 25, 2012 4:17 pm 
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Joined: Thu Sep 24, 2009 10:59 am
Posts: 5922
Where has this question come from? Surely it needs some brackets to be answerable? And is it really an 11+ question? Ugh.


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 Post subject: Re: Help with sum
PostPosted: Sat Aug 25, 2012 4:24 pm 
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Joined: Fri Jun 22, 2012 11:45 pm
Posts: 19
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.


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 Post subject: Re: Help with sum
PostPosted: Sat Aug 25, 2012 4:44 pm 
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Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6962
Location: East Kent
The papers set by GL assessment do not require Bodmas, you work from left to right.

Where was this question from Beckii330?


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 Post subject: Re: Help with sum
PostPosted: Sat Aug 25, 2012 7:54 pm 
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Joined: Thu Jun 14, 2012 9:28 am
Posts: 121
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


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 Post subject: Re: Help with sum
PostPosted: Sun Aug 26, 2012 5:06 pm 
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Joined: Tue May 29, 2012 8:16 pm
Posts: 57
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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