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PostPosted: Sat Oct 11, 2008 4:55 pm 
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Joined: Sun May 11, 2008 8:55 pm
Posts: 12
I am confused with this question.

The diagram shows a circle with circumference of 1 cm being rolled around an equilateral triangle with sides of 1 cm length. How many complete turns does the circle make as it rolls around the triangle (without slipping) to it's original starting position.

The correct answer is 4, however I thought that the answer was 3. Can anyone please explain the logic here?

Thanks in advance


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PostPosted: Sat Oct 11, 2008 5:51 pm 
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Joined: Sat Nov 24, 2007 11:09 pm
Posts: 218
Hi

This is from last year (2008) Math paper. I hope the following info helps

viewtopic.php?t=5383


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PostPosted: Sun Oct 12, 2008 10:47 am 
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Joined: Fri Oct 12, 2007 12:42 pm
Posts: 3810
Location: Chelmsford and pleased
This is a problem from the junior maths challenge, aimed at bright year 8 pupils.

The penny has to turn the corners, it doesn't jump. If you roll a real penny around a triangle, with a dot on the penny at the corner, you can see how it turns 1/3 of a turn.

Horrid question, I tell my pupils to have a go at the last question on the paper and not to worry too much if they can't do it.

Drawing always helps.


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 Post subject: quite difficult
PostPosted: Thu Oct 16, 2008 8:59 pm 
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Joined: Sun May 11, 2008 8:55 pm
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It is indeed quite difficult question. I took some time to understand, but now can explain it to my daughter. Thanks a lot


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PostPosted: Wed Dec 24, 2008 7:50 am 
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Joined: Wed Dec 24, 2008 6:21 am
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I took the exam with this question. We bought the past paper for my brother to practice as he is doing it next year. I put 3 and got it wrong. The answer booklet says it is 4 but I have no idea why. I still got in though! :roll:

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