Help with Essex 11+ Maths 2005 paper Question 26

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NikeLocs
Posts: 5
Joined: Thu Sep 20, 2012 8:42 am

Help with Essex 11+ Maths 2005 paper Question 26

Post by NikeLocs »

Can anyone help me solve this question please. A four side polygon has two diagonals. If a polygon has 9 diagonals how many sides does it have?
My husband and daughter both came up with 18 (I am rubbish at maths, so didn't even attempt it). According to the marking scheme the answer is 6.

I will be grateful for an axplanation as to how to calculate number of sides from diagonals given and vice versa.

Thank you
moved
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Location: Chelmsford and pleased

Re: Help with Essex 11+ Maths 2005 paper Question 26

Post by moved »

I get children to draw this one out.

3 sides 0 diagonals
4 sides 2 diagonals
5 sides 5 diagonals
6 sides 9 diagonals

There is a formula but it is beyond most 11 year olds

n(n - 3)/2

n is the number of sides, so for a six sided shape we have
6(6 - 3)/2
6 x 3 / 2
18/2 = 9
peter doe
Posts: 14
Joined: Sun Sep 09, 2012 9:28 am

Re: Help with Essex 11+ Maths 2005 paper Question 26

Post by peter doe »

Thanks moved ,I actually thought the question was moved ..lol

@OP just as moved mentioned I think this is one in which they will have to use their memory ,just like they normally do for lines of symmetry ..I've come across that kind of question several times and have never seen one that needed the algebraic formula to solve .It's more about testing their ability to solve simple word problems using knowledge they've acquired over the school years .
Okanagan
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Joined: Mon Aug 22, 2011 9:20 pm
Location: Warwickshire

Re: Help with Essex 11+ Maths 2005 paper Question 26

Post by Okanagan »

See the explanation posted recently here: http://www.elevenplusexams.co.uk/forum/ ... 73#p322873
NikeLocs
Posts: 5
Joined: Thu Sep 20, 2012 8:42 am

Re: Help with Essex 11+ Maths 2005 paper Question 26

Post by NikeLocs »

Thank you very much, moved, peter doe and okanagan. I'll pass this on to my husband. :)
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