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2002 UK Senior Mathematical Challenge, question
14:
A circular disc of diameter d rolls without slipping
around the inside of a ring of internal diameter 3d, as shown in
the diagram. By the time that the centre of the inner disc returns
to its original position for the first time, how many times will
the inner disc have turned about its centre?
A: 1
B: pi
C: 3
D: 2pi
E: 2
This dynamic construction helps students appreciate
why the answer is NOT response C: 3, which is the intuitively correct
answer!
Have a play and conclude for yourself what the right
response is!
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