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Coke Machine

The coke machine in college takes 50 pence pieces. It also takes a certain foreign coin of traditional design...

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Rotating Triangle

What happens to the perimeter of triangle ABC as the two smaller circles change size and roll around inside the bigger circle?

All Tied Up

Stage: 4 Challenge Level: Challenge Level:2 Challenge Level:2

The problem "The Spider and the Fly" is worth trying first if you do not know where to start.