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Building Tetrahedra

Can you make a tetrahedron whose faces all have the same perimeter?

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Rudolff's Problem

A group of 20 people pay a total of £20 to see an exhibition. The admission price is £3 for men, £2 for women and 50p for children. How many men, women and children are there in the group?

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Show that for any triangle it is always possible to construct 3 touching circles with centres at the vertices. Is it possible to construct touching circles centred at the vertices of any polygon?

Overturning Fracsum

Age 14 to 16 Challenge Level:

Solve the following system of equations to find the values of $x$, $y$ and $z$. $${xy\over (x+y)}=1/2$$ $${yz\over (y+z)} =1/3$$ $${xz\over (x+z)} = 1/7$$