You have been given nine weights, one of which is slightly heavier than the rest. Can you work out which weight is heavier in just two weighings of the balance?

Here is a solitaire type environment for you to experiment with. Which targets can you reach?

Using the interactivity, can you make a regular hexagon from yellow triangles the same size as a regular hexagon made from green triangles ?

If the yellow equilateral triangle is taken as the unit for area, what size is the hole ?

If you think that mathematical proof is really clearcut and universal then you should read this article.

Solve the equations to identify the clue numbers in this Sudoku problem.