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Just Rolling Round

P is a point on the circumference of a circle radius r which rolls, without slipping, inside a circle of radius 2r. What is the locus of P?

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Pericut

Two semicircle sit on the diameter of a semicircle centre O of twice their radius. Lines through O divide the perimeter into two parts. What can you say about the lengths of these two parts?

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Giant Holly Leaf

Find the perimeter and area of a holly leaf that will not lie flat (it has negative curvature with 'circles' having circumference greater than 2πr).

Two Shapes & Printer Ink

Stage: 4 Challenge Level: Challenge Level:1
Some solution we were offered cleverly reasoned that the grid, offered in the Hint as an approximation, was in fact completely accurate at the pixel level - which for printer ink is what counts. Sometimes we explore mathematics in unreal perfection for the sake of the thinking that will draw us into. Other solutions did this:

"You can split the problem up into combinations of circular shapes, each of which we can find the area of. Doing this I foundthat the star is over 5% larger than the S shape."


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. More information on many of our other activities can be found here.
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