Help with VR

[FreddySam]

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?

[yoyo123]

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?

[FreddySam]

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.

[stevew61]

Have a look at the Susan J. Daughtrey method & technique books.

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" onclick="window.open(this.href);return false;
.

[999 mum]

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!)

[tokyonambu]

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/" onclick="window.open(this.href);return false;

http://en.wikipedia.org/wiki/Subset_sum_problem" onclick="window.open(this.href);return false;