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 Post subject: Help with VR
PostPosted: Tue Jun 07, 2011 5:29 pm 
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Joined: Tue Jun 07, 2011 12:37 pm
Posts: 14
Can anyone tell me how to approach the following style question:

Use three of the numbers on the left once only to make up the number you are given.

7,9,11,13,16 : 31= ( + + )

My daughter didn't know where to start with these - are there any techniques I can tell her to use?


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 Post subject: Re: Help with VR
PostPosted: Tue Jun 07, 2011 5:35 pm 
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Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6966
Location: East Kent
I would try trial and error to begin with.
16 + 13 = 29 ..can;t be those two as there is no 2 etc. afetr a while she will get a feel for which numbers are likely. Lots of practice.

I haven;t seen examples like this before.

Where are you based?
Is this a multiple choice question or standard?


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 Post subject: Re: Help with VR
PostPosted: Tue Jun 07, 2011 5:46 pm 
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Joined: Tue Jun 07, 2011 12:37 pm
Posts: 14
Thanks for replying so quickly!
We live in Lincolnshire. It is standard format and so can be very time consuming! I haven't seen many of these type of questions either, maybe they are just specific to Lincs. Maths is not my daughter's strong point which is why I'm a bit worried.


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 Post subject: Re: Help with VR
PostPosted: Tue Jun 07, 2011 6:05 pm 
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Joined: Fri Nov 17, 2006 8:54 pm
Posts: 1770
Location: caversham
Have a look at the Susan J. Daughtrey method & technique books.

Quote:
Books 1, 2, 3 and 4 cover the TECHNIQUE and PRACTICE of each of the 35 Types of question. Book 1 covers the first 13 Types, book 2 covers 10 Types and the remaining Types are dealt with in books 3 and 4 deals specifically with maths and code questions.


http://www.elevenplusexams.co.uk/books/list.php?g=f&p=7
.


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 Post subject: Re: Help with VR
PostPosted: Tue Jun 07, 2011 6:38 pm 
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Joined: Sat Feb 13, 2010 11:02 pm
Posts: 420
staffakh wrote:
Can anyone tell me how to approach the following style question:

Use three of the numbers on the left once only to make up the number you are given.

7,9,11,13,16 : 31= ( + + )


hi,

I have not come across this type of question before, but I would suggest that you take one number away from the 31 and then see if the remainder can be made by two of the other numbers.

eg, 31-7 = 24, can 24 be made by two others?

31- 9= 22, can 22 be made by two others?

31- 11= 20, can 20 be made by two others? 7+13 = 20

so the answer is 7+13+11 (I think!)


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 Post subject: Re: Help with VR
PostPosted: Thu Jun 09, 2011 3:47 pm 
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Joined: Thu Oct 21, 2010 4:38 pm
Posts: 109
The question "which numbers from this list add up to this number?" turns out to be, in general, extremely hard and very interesting. It's nice to have a problem which is simple enough, in a small example, to make an 11+ question, but leads on to some fairly challenging (undergraduate, or possibly just on the outer limits of A Level) theory by just adding some more numbers to the question.

Suppose I gave you a hundred numbers and asked you to choose the ones that added up to some other number. How long did it take you? Now, suppose I give you a thousand numbers and give you ten times longer than it took with a hundred numbers. Can you do it?

Manage that and you're well on your way to a million dollars. No, really, a million dollars.

http://www.claymath.org/millennium/P_vs_NP/

http://en.wikipedia.org/wiki/Subset_sum_problem


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