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 Post subject: CSSE 2008 maths paper help!Posted: Sun Aug 12, 2012 2:15 pm

Joined: Wed Mar 09, 2011 2:22 pm
Posts: 710
I don't understand the given answer to the final question on this paper!! Does anyone remember this one from having looked at past papers? I'll write it out here...

The diagram shows a circle with circumference of 1cm being rolled around an equilateral triangle with sides of length 1cm.

How may complete turns does the circle make as it rolls around the triangle (without slipping) to its original starting position?

What do you think??

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 Post subject: Re: CSSE 2008 maths paper help!Posted: Sun Aug 12, 2012 2:22 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8598
Manana wrote:
I don't understand the given answer to the final question on this paper!! Does anyone remember this one from having looked at past papers? I'll write it out here...

The diagram shows a circle with circumference of 1cm being rolled around an equilateral triangle with sides of length 1cm.

How may complete turns does the circle make as it rolls around the triangle (without slipping) to its original starting position?

What do you think??

I would have thought 3.. is that the answer?

the circumference of the circle is one cm and hence if rolled round the edges would go 1cm to get it back a complete circle. The total length of the sides of the triangle is 3cms so 3 revolutions?

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 Post subject: Re: CSSE 2008 maths paper help!Posted: Sun Aug 12, 2012 3:09 pm

Joined: Wed Mar 09, 2011 2:22 pm
Posts: 710
hermanmunster wrote:
Manana wrote:
I don't understand the given answer to the final question on this paper!! Does anyone remember this one from having looked at past papers? I'll write it out here...

The diagram shows a circle with circumference of 1cm being rolled around an equilateral triangle with sides of length 1cm.

How may complete turns does the circle make as it rolls around the triangle (without slipping) to its original starting position?

What do you think??

I would have thought 3.. is that the answer?

the circumference of the circle is one cm and hence if rolled round the edges would go 1cm to get it back a complete circle. The total length of the sides of the triangle is 3cms so 3 revolutions?

Yes-DS, DH and I all thought 3, but the answer sheet says 4?! It's a 2 mark question as well?!!

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 Post subject: Re: CSSE 2008 maths paper help!Posted: Sun Aug 12, 2012 3:15 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8598
hmmm - sounds like time for some gooogling:

4!! we weren't allowing for having to do a 360 degree turn at the corners ! Duh!

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 Post subject: Re: CSSE 2008 maths paper help!Posted: Sun Aug 12, 2012 4:29 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 13994
Every shape will have an extra 'turn' because the external angles of a shape are 360 degrees.

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 Post subject: Re: CSSE 2008 maths paper help!Posted: Mon Aug 13, 2012 9:33 am

Joined: Wed Mar 09, 2011 2:22 pm
Posts: 710
hermanmunster wrote:
hmmm - sounds like time for some gooogling:

4!! we weren't allowing for having to do a 360 degree turn at the corners ! Duh!

Doh-yes, of course! That makes perfect sense to me as a 35 year old (who has seen the answer and had it explained to me!); I will see what DS says!!

I sort of imagined it pivoting at the corners but obviously didn't think deeply enough about it!

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