Solve this Sudoku puzzle whose clues are in the form of sums of the numbers which should appear in diagonal opposite cells.

Have a go at this game which has been inspired by the Big Internet Math-Off 2019. Can you gain more columns of lily pads than your opponent?

This article for teachers describes several games, found on the site, all of which have a related structure that can be used to develop the skills of strategic planning.

Can you put the 25 coloured tiles into the 5 x 5 square so that no column, no row and no diagonal line have tiles of the same colour in them?

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

Hover your mouse over the counters to see which ones will be removed. Click to remove them. The winner is the last one to remove a counter. How you can make sure you win?

60 pieces and a challenge. What can you make and how many of the pieces can you use creating skeleton polyhedra?

A game for 2 people. Take turns placing a counter on the star. You win when you have completed a line of 3 in your colour.

This task encourages you to investigate the number of edging pieces and panes in different sized windows.

Can you find all the different ways of lining up these Cuisenaire rods?

How many triangles can you make using sticks that are 3cm, 4cm and 5cm long?

Place the numbers 1 to 6 in the circles so that each number is the difference between the two numbers just below it.

How can you put five cereal packets together to make different shapes if you must put them face-to-face?

Can you work out how to balance this equaliser? You can put more than one weight on a hook.

Use the interactivity to find all the different right-angled triangles you can make by just moving one corner of the starting triangle.

What is the smallest cuboid that you can put in this box so that you cannot fit another that's the same into it?

How many models can you find which obey these rules?

Add or subtract the two numbers on the spinners and try to complete a row of three. Are there some numbers that are good to aim for?

Here are some rods that are different colours. How could I make a dark green rod using yellow and white rods?

Can you arrange the digits 1, 1, 2, 2, 3 and 3 to make a Number Sandwich?

A tetromino is made up of four squares joined edge to edge. Can this tetromino, together with 15 copies of itself, be used to cover an eight by eight chessboard?

Have a go at this well-known challenge. Can you swap the frogs and toads in as few slides and jumps as possible?

Find out what a "fault-free" rectangle is and try to make some of your own.

Can you find all the different triangles on these peg boards, and find their angles?

How many different triangles can you draw on the dotty grid which each have one dot in the middle?

Is it possible to place 2 counters on the 3 by 3 grid so that there is an even number of counters in every row and every column? How about if you have 3 counters or 4 counters or....?

You have 4 red and 5 blue counters. How many ways can they be placed on a 3 by 3 grid so that all the rows columns and diagonals have an even number of red counters?

Can you make a train the same length as Laura's but using three differently coloured rods? Is there only one way of doing it?

Can you put the numbers from 1 to 15 on the circles so that no consecutive numbers lie anywhere along a continuous straight line?

Here are four cubes joined together. How many other arrangements of four cubes can you find? Can you draw them on dotty paper?

How many trains can you make which are the same length as Matt's, using rods that are identical?

The NRICH team are always looking for new ways to engage teachers and pupils in problem solving. Here we explain the thinking behind maths trails.

Use the interactivity to help get a feel for this problem and to find out all the possible ways the balls could land.

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.

This problem is based on a code using two different prime numbers less than 10. You'll need to multiply them together and shift the alphabet forwards by the result. Can you decipher the code?

What is the best way to shunt these carriages so that each train can continue its journey?

How many different triangles can you make on a circular pegboard that has nine pegs?

Can you shunt the trucks so that the Cattle truck and the Sheep truck change places and the Engine is back on the main line?

How will you go about finding all the jigsaw pieces that have one peg and one hole?

There is a long tradition of creating mazes throughout history and across the world. This article gives details of mazes you can visit and those that you can tackle on paper.

In this article, the NRICH team describe the process of selecting solutions for publication on the site.

Place the numbers 1 to 10 in the circles so that each number is the difference between the two numbers just below it.

Try out the lottery that is played in a far-away land. What is the chance of winning?

Use the information to describe these marbles. What colours must be on marbles that sparkle when rolling but are dark inside?

Ben and his mum are planting garlic. Use the interactivity to help you find out how many cloves of garlic they might have had.

Can you put the numbers 1 to 8 into the circles so that the four calculations are correct?

What do the numbers shaded in blue on this hundred square have in common? What do you notice about the pink numbers? How about the shaded numbers in the other squares?

If you hang two weights on one side of this balance, in how many different ways can you hang three weights on the other side for it to be balanced?