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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?

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Just Opposite

A and C are the opposite vertices of a square ABCD, and have coordinates (a,b) and (c,d), respectively. What are the coordinates of the vertices B and D? What is the area of the square?

Coke Machine

Stage: 4 Challenge Level: Challenge Level:1

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

Coins inserted into the machine slide down a chute into the machine and a drink is duly released.

How many more revolutions does the foreign coin make over the 50 pence piece going down the chute?