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Diagram of problem A length of thin wire ($L$ ) binds together two cylindrical welding rods, whose radii are $R$ and $r$ , by passing all the way around them both.

Find $L$ in terms of $R$ and $r$.

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The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.

NRICH is part of the family of activities in the Millennium Mathematics Project.

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