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PostPosted: Thu Aug 20, 2009 12:20 am 
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Joined: Sat Nov 17, 2007 8:55 pm
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Location: Bexley
My son is working slowly through the Bond 10 minute maths tests. I didn't have these for my older children and I'm a bit alarmed by some of the algebra in there.

My son gets basic algebra without too much effort, and I hoped that would be enough for the 11+. However, he (and I!) are a bit thrown by questions like, "If 7x - 9 = 10x - 18, what is the value of x?"

We're told that in Bexley there won't be any algebra on the maths paper as children won't have covered that at school. However, I know that algebra does appear in the Kent test (which he's also doing). My question is, do people think there will be questions as hard as this in the Kent test? If so, can anyone give me a simple method for working out this type of question? My son and I couldn't get our heads round the explanation offered by older brother!


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PostPosted: Thu Aug 20, 2009 12:52 am 
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Joined: Thu Aug 20, 2009 12:42 am
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Location: West Malling
Quote:
My son gets basic algebra without too much effort, and I hoped that would be enough for the 11+. However, he (and I!) are a bit thrown by questions like, "If 7x - 9 = 10x - 18, what is the value of x?"

You need to group the x's and the numbers separately. If you move anything across the =sign it changes from +ve to -ve and visa versa, so:
7x - 9 = 10x -18
18 - 9 = 10x - 7x
9 = 3x
9/3 = x
3 = x

From what I've seen there will be questions like this in the Kent test, but my son's school hasn't taught them how to do these yet!!


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PostPosted: Thu Aug 20, 2009 9:44 am 
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Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6966
Location: East Kent
Look at The Tutors CD1 maths free demo

http://www.elevenplusexams.co.uk/cd/demo-ttu-math-1/f0/

This has 5 questions on algebra which will show you the type of algebra questions which may be in teh Kent test.


There was a dicussion a while back

viewtopic.php?t=9862

and

viewtopic.php?t=9778


try this too
http://www.gamequarium.com/algebra.htm


I can recommend the Usborne Illustrated Dictionary of Maths too.


Hope this helps.


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PostPosted: Thu Aug 20, 2009 12:04 pm 
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Joined: Tue Dec 13, 2005 12:49 pm
Posts: 1647
Location: berkshire
Quote:
If 7x - 9 = 10x - 18, what is the value of x


This is probably not the 'correct' way of doing it but it is simple and it works.

You must get all the 'x' values on to the same side of the '=' and all the 'number' values on the other side (it helps if each are a positive number).... so ...

7x - 9 = 10x - 18

My first thought would be that 10x is higher than 7x so I will move the 7x over to the right hand side. to do this the 'sign' changes from a positive to a negative (Yes I know the correct terminology is what you do to one side you do to the other so I will try and explain that way next)


-9 = 10x - 7x - 18
(the positive 7x and changed to a negative 7x on the other side)

So now I need the -18 to move to the left (It will become a positive)

18 - 9 =10x - 7x

9 = 3x

Divide both by three gives 3= x

Okay
The 'other' way

Quote:
If 7x - 9 = 10x - 18, what is the value of x


What you do to one side you do to the other.... and we want to be left with x = 'a value'

7x - 9 = 10x - 18

To leave the numbers on the left you have to take 7x from both sides

-9 = 10x - 18 - 7x

To take the - 18 out of both side then you have to minus -18

Therefore -9 - (-18 ) = 10x - 7x

a - (-18 ) is the same as +18

so

-9 +18 = 10x - 7x

9 = 3x (to get to x you have to divide both sides by 3)

9/3 = x

3 = x

If you move the x and values to the other side it would still work out but you would be left with

-3 = -x therefore 3 = x


If you can understand that then well done!

I also recommend the Usborne Illustrated dictionary of Maths....... great examples .... covers all KS3 topics


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PostPosted: Thu Aug 20, 2009 1:21 pm 
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Joined: Sat Nov 17, 2007 8:55 pm
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Location: Bexley
Many thanks for everyone's replies. I've just been looking at a WHSmith book on algebra and they seem to suggest the following method:

7x-9 = 10x-18
take 7x from both sides which leaves you with:
-9 = 3x-18
take 18 from both sides which leaves you with:
9 = 3x
Therefore x=3

(that's the condensed version!)

But I'm still wondering if there really will be this type of question in the Kent test. This type doesn't appear in the tutors' free maths demo. So long as you can grasp the basic concept of letters representing numbers, I think it's possible for an intelligent child to visualise the answer to those types of algebra questions which do appear in the maths demo. The type I've mentioned above is obviously KS3 work and seems to me to be something you just wouldn't be able to tackle without having been taught a method, which is very unfair for children who haven't been prepared for the tests.

We're now in the "boosting confidence" stage so I'm a bit reluctant to introduce a new concept at this stage. Another son did the Kent test in January last year and came out saying that he'd missed out ALL the algebra questions! He had a real thing about algebra and just refused to tackle them, even though I'd spent time with him beforehand explaining that they weren't as hard as they looked. But he still passed so I guess that means there weren't too many!


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PostPosted: Thu Aug 20, 2009 1:56 pm 
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Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6966
Location: East Kent
they may appear in the type of question where they give you an expression

There are 5 rearranged expressions and you have to say which is wrong.

e.g
a=1/2b

which of following is wrong
2a=b
b/a=2
1/2a=b
a/b=2
b=2/a


also 4x+2=30-3x

find the value of x



if he really can;t get them, don't panic itis only a couple of marks in the whole paper. Just make an intelligent guess.


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PostPosted: Thu Aug 20, 2009 11:19 pm 
I would say that teaching them the correct method (as in what secondary will do with them) takes longer than the question warrants in that such a question is unlikely to appear.

For my pupils, I suggest they guess using subsitution, then alter guess according to how far off they are. Start at 1 because answer is going to be low and a whole number at this stage.

i.e. Try 1 no, 7-9 does not equal 10-18
Try 2 no, 14-9 does not = 20-18 but you are getting closer
Try, 3 bingo, 21-9 = 30-18


This is probably easier for them (they should at least be able to substitute for questions such as if 3x - 4 = 11, what is x) and potentially quicker than going through the proper algebraic steps.


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PostPosted: Fri Aug 21, 2009 9:48 am 
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Location: Bexley
FM - thanks, that's reassuring. I'd just come to that conclusion myself. What I was forgetting of course was that, with the Bond 10 minute tests you have to work the answer out, whereas my son will be doing multiple choice questions so will have 5 possible answers. It will probably be less confusing for him to just try out each of the answers until he finds the one that fits!


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PostPosted: Fri Aug 21, 2009 9:53 pm 
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Joined: Thu Oct 11, 2007 9:21 pm
Posts: 181
Location: Medway/Kent
I have always struggled with algebra and find it hard to think that our 10 year olds would have to know how to approach this type of question.

In my area the most I would teach at this stage would be to use the multiple choice answer sheet and use the possible answers to "test" to see which one fits. Saying that though this does take time and my first reaction is to guess the answer first time round and come back to it if there is time at the end.

I know that this reponse may draw shock from the fori=um baut they are 10 after all!
reddebs

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PostPosted: Fri Aug 21, 2009 11:49 pm 
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Location: Bexley
Reddebs - I like that approach! I find it absolutely appalling that algebra appears on eleven plus papers when it's not even part of the KS2 maths syllabus.


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