Step back and reflect! This article reviews techniques such as substitution and change of coordinates which enable us to exploit underlying structures to crack problems.

A pair of Sudoku puzzles that together lead to a complete solution.

Four small numbers give the clue to the contents of the four surrounding cells.

This Sudoku, based on differences. Using the one clue number can you find the solution?

This Sudoku problem consists of a pair of linked standard Suduko puzzles each with some starting digits

Problem solving is at the heart of the NRICH site. All the problems give learners opportunities to learn, develop or use mathematical concepts and skills. Read here for more information.

A small circle in a square in a big circle in a trapezium. Using the measurements and clue given, find the area of the trapezium.

A random ramble for teachers through some resources that might add a little life to a statistics class.

How many generations would link an evolutionist to a very distant ancestor?

Using the 8 dominoes make a square where each of the columns and rows adds up to 8

All the words in the Snowman language consist of exactly seven letters formed from the letters {s, no, wm, an). How many words are there in the Snowman language?

From the atomic masses recorded in a mass spectrometry analysis can you deduce the possible form of these compounds?

Can you use your powers of logic and deduction to work out the missing information in these sporty situations?

A particular technique for solving Sudoku puzzles, known as "naked pair", is explained in this easy-to-read article.

By inscribing a circle in a square and then a square in a circle find an approximation to pi. By using a hexagon, can you improve on the approximation?

Like all sports rankings, the cricket ratings involve some maths. In this case, they use a mathematical technique known as exponential weighting. For those who want to know more, read on.

In how many different ways can I colour the five edges of a pentagon red, blue and green so that no two adjacent edges are the same colour?