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### Number and algebra

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# Concrete Calculation

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### Just Rolling Round

### Coke Machine

### Just Opposite

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Nurturing young mathematicians: teacher webinars

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Age 14 to 16

Challenge Level

The builders have dug a hole in the ground to be filled with concrete for the foundations of our garage. The shape is designed to avoid subsidence that might be caused by the roots of some very large trees nearby. The hole is perfectly symmetrical with vertical walls, 1.2 metres high, surrounding a rectangular area measuring 6 metres by 5 metres. A mound of earth in the centre, the shape of the frustum of a pyramid, has a rectangular base 4.8 metres by 3.8 metres and a horizontal rectangular top 3.8 metres by 2.8 metres. The height of this mound is 0.9 metres. How many cubic metres of ready-mix concrete should the builders order to fill this hole to make the concrete raft for the foundations? Can you explain the method simply to help the builders to do the calculations for similar shaped rafts of other dimensions?

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?

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

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?