11 Plus Exams Forum

Question 26 Maths - 2008
Please can someone help with this question.

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

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



Thanks

there is a thread that explains it all further down the board , the circle basically turns an additional 1/3 of a turn at each corner to negotitate the turn without covering any ground on the triangle in addition to the obvious 3 rotations along each side - v tough question and for kids of this age its pretty ridiculous

Thanks.
I'll see if I can find the thread.

Thanks a lot for finding the thread.
This particular questions has really bothered me. I couldn't just figure out how they got 4. I just got stuck on 3.
Thanks

A very visual way of doing this question is to put a blob of tipex on a penny. Draw a triangle and watch what happens at the corners. I drew it out for one of my pupils. We then played with a square, straight line etc.