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?

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....?

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?

Can you work out how many cubes were used to make this open box? What size of open box could you make if you had 112 cubes?

10 space travellers are waiting to board their spaceships. There are two rows of seats in the waiting room. Using the rules, where are they all sitting? Can you find all the possible ways?

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.

Design an arrangement of display boards in the school hall which fits the requirements of different people.

How many ways can you find to do up all four buttons on my coat? How about if I had five buttons? Six ...?

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?

Rather than using the numbers 1-9, this sudoku uses the nine different letters used to make the words "Advent Calendar".

A few extra challenges set by some young NRICH members.

Cut four triangles from a square as shown in the picture. How many different shapes can you make by fitting the four triangles back together?

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

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

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

Each of the main diagonals of this sudoku must contain the numbers 1 to 9 and each rectangle width the numbers 1 to 4.

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?

Can you find all the ways to get 15 at the top of this triangle of numbers? Many opportunities to work in different ways.

Only one side of a two-slice toaster is working. What is the quickest way to toast both sides of three slices of bread?

There are nine teddies in Teddy Town - three red, three blue and three yellow. There are also nine houses, three of each colour. Can you put them on the map of Teddy Town according to the 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?

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.

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

What could the half time scores have been in these Olympic hockey matches?

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.

The puzzle can be solved with the help of small clue-numbers which are either placed on the border lines between selected pairs of neighbouring squares of the grid or placed after slash marks on. . . .

Swap the stars with the moons, using only knights' moves (as on a chess board). What is the smallest number of moves possible?

This pair of linked Sudokus matches letters with numbers and hides a seasonal greeting. Can you find it?

Mr McGregor has a magic potting shed. Overnight, the number of plants in it doubles. He'd like to put the same number of plants in each of three gardens, planting one garden each day. Can he do it?

Place the numbers 1 to 8 in the circles so that no consecutive numbers are joined by a line.

The number of plants in Mr McGregor's magic potting shed increases overnight. He'd like to put the same number of plants in each of his gardens, planting one garden each day. How can he do it?

There are seven pots of plants in a greenhouse. They have lost their labels. Perhaps you can help re-label them.

Can you fill in this table square? The numbers 2 -12 were used to generate it with just one number used twice.

A Sudoku that uses transformations as supporting clues.

The letters of the word ABACUS have been arranged in the shape of a triangle. How many different ways can you find to read the word ABACUS from this triangular pattern?

Investigate the smallest number of moves it takes to turn these mats upside-down if you can only turn exactly three at a time.

Sweets are given out to party-goers in a particular way. Investigate the total number of sweets received by people sitting in different positions.

In this game for two players, you throw two dice and find the product. How many shapes can you draw on the grid which have that area or perimeter?

How long does it take to brush your teeth? Can you find the matching length of time?

Can you recreate these designs? What are the basic units? What movement is required between each unit? Some elegant use of procedures will help - variables not essential.

Different combinations of the weights available allow you to make different totals. Which totals can you make?

A cinema has 100 seats. Show how it is possible to sell exactly 100 tickets and take exactly £100 if the prices are £10 for adults, 50p for pensioners and 10p for children.

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?

Bellringers have a special way to write down the patterns they ring. Learn about these patterns and draw some of your own.