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# Rolling a coin part 2

## Question

Hopefully I don't ruin the question this time.

Assume that we have two coins that are not identical in size but are both perfect circles. We want to roll a coin along the edge of another coin where the moving coin starts at 1 side and ends up on the exact opposite side (only traveling half of the non-moving coin) and still end up in the same starting position (the moving-coin's orientation ends in the same position it started).

What size(s) must the moving coin have relative to the non-moving coin?

If we want the moving coin to travel 3/4's around the non-moving coin and still end up in its starting position, what sizes for the moving coin work?

## 3 answers to this question

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The moving coin should be smaller than the stationary coin and their sizes must have ratios of 1:3 or 1:5 or 1:<any odd number>

Need more time for the 3/4 case.

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The moving coin should be smaller than the stationary coin and their sizes must have ratios of 1:3 or 1:5 or 1:<any odd number>

Need more time for the 3/4 case.

isn't it any even number?

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R=8/3*r, 16/3*r, 24/3*r etc R=8/3*x*r x is natural

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