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 Post subject: Tricky maths question
PostPosted: Fri Jan 05, 2007 6:51 pm 
This is a question from an independent school maths practise paper, my daughter cannot solve it and neither can I.

You are given a grid with 9 squares (3 across, 3 down etc). You have to insert the figures 2, 2, 2, 3, 3, 3, 4, 4, 4 - so that each line, including diagonally, adds up to nine. I can't do it. Is it a trick question or am I missing something?

Thank you.


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 Post subject:
PostPosted: Fri Jan 05, 2007 7:42 pm 
I can do this so everything adds up except one diagonal. I can't get that last diagonal to add up to 9. Are you sure it included diagonals?


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 Post subject:
PostPosted: Fri Jan 05, 2007 7:50 pm 
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Joined: Fri Mar 17, 2006 5:12 pm
Posts: 1301
Location: Birmingham
The trick is to recognise that there are only 2 combinations of 3 numbers from the set that add up to 9, Either 2,3,4 or 3,3,3.

You need to recognise that having a different combination of 2,3 &4 in the rows (and columns ) will give the desired results for the rows and columns, but the only way the diagonals will add up to 9 is if one of these is 3, 3 & 3.

So start out by populating one of the diagonals with 3s and then just make sure the each of the rows has a different permutation. viz.

3xx
x3x
xx3

342
234
423

Ken


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PostPosted: Fri Jan 05, 2007 7:52 pm 
Absolutely sure about the diagonals, that is the problem we had as well. I think it might be a trick question, though nothing in the question gives a clue that it might be - I suppose it could be a mistake. It is from the Emmanuel school in London.


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 Post subject:
PostPosted: Fri Jan 05, 2007 7:54 pm 
Thank you Ken R. I can't believe I never thought of that. You are brilliant!


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 Post subject:
PostPosted: Fri Jan 05, 2007 7:54 pm 
well KenR aren't you the clever one. I'll have to try that question out on my little darling now.


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 Post subject:
PostPosted: Fri Jan 05, 2007 8:24 pm 
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Joined: Fri Mar 17, 2006 5:12 pm
Posts: 1301
Location: Birmingham
I've had lots of practice having gone through every paper I could find last year with my son. So I am fairly confident that I could now pass my 11+ second time round!

I found the Independent school exams are quite different to the normal 11+ grammar exams, the maths questions in particular seem to be graduated and get quite hard towards the end. I guess this is to test the scholarship level candidates.

I recall a practice paper we were sent from Solihull School last year which had a tough question about a boat and a hovercraft going in different directions and speeds around a lake. The candidates had to work out when the boat/hovercraft would pass and how far they had travelled.

The best way to work it out was by using algebra but strictly speaking they shouldn't have done this at KS2.


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PostPosted: Fri Jan 05, 2007 8:44 pm 
The boat question can be done by thinking about relative speeds - if one is going 20 mph and the other 10 mph in the opposite direction they are approaching each other at 30 mph. So to meet you only have to think about one moving half way round at 30 mph - no algebra needed!


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 Post subject:
PostPosted: Sat Jan 06, 2007 1:01 pm 
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Joined: Thu Nov 02, 2006 3:07 pm
Posts: 1149
Location: Finchley - Barnet
I gave this to my own little darling, who did it in less that 50 secs! :D I feel rather humilated for myself.... :shock:

INEX


Anonymous wrote:
well KenR aren't you the clever one. I'll have to try that question out on my little darling now.

_________________
sj355


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 Post subject:
PostPosted: Sat Jan 06, 2007 3:31 pm 
Quote:
I've had lots of practice having gone through every paper I could find last year with my son. So I am fairly confident that I could now pass my 11+ second time round!


I gave this to both my little darlings (boys) and my big darling and all managed easily in under a minute. Maybe its just mum who's thick - despite a grammar school education!!


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