Make one big triangle so the numbers that touch on the small triangles add to 10.

This 100 square jigsaw is written in code. It starts with 1 and ends with 100. Can you build it up?

Can you see why 2 by 2 could be 5? Can you predict what 2 by 10 will be?

Players take it in turns to choose a dot on the grid. The winner is the first to have four dots that can be joined to form a square.

Take it in turns to make a triangle on the pegboard. Can you block your opponent?

These interactive dominoes can be dragged around the screen.

Use your mouse to move the red and green parts of this disc. Can you make images which show the turnings described?

How can the same pieces of the tangram make this bowl before and after it was chipped? Use the interactivity to try and work out what is going on!

What is the greatest number of squares you can make by overlapping three squares?

Investigate how the four L-shapes fit together to make an enlarged L-shape. You could explore this idea with other shapes too.

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

Can you find a reliable strategy for choosing coordinates that will locate the treasure in the minimum number of guesses?

Take it in turns to place a domino on the grid. One to be placed horizontally and the other vertically. Can you make it impossible for your opponent to play?

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

If you have only four weights, where could you place them in order to balance this equaliser?

If you can post the triangle with either the blue or yellow colour face up, how many ways can it be posted altogether?

Move just three of the circles so that the triangle faces in the opposite direction.

Investigate which numbers make these lights come on. What is the smallest number you can find that lights up all the lights?

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?

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?

Can you work out what is wrong with the cogs on a UK 2 pound coin?

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?

A game for 1 person. Can you work out how the dice must be rolled from the start position to the finish? Play on line.

Can you put these shapes in order of size? Start with the smallest.

A game for 1 or 2 people. Use the interactive version, or play with friends. Try to round up as many counters as possible.

A shape and space game for 2,3 or 4 players. Be the last person to be able to place a pentomino piece on the playing board. Play with card, or on the computer.

Start by putting one million (1 000 000) into the display of your calculator. Can you reduce this to 7 using just the 7 key and add, subtract, multiply, divide and equals as many times as you like?

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?

Imagine a wheel with different markings painted on it at regular intervals. Can you predict the colour of the 18th mark? The 100th mark?

Use the interactivity to find out how many quarter turns the man must rotate through to look like each of the pictures.

Each light in this interactivity turns on according to a rule. What happens when you enter different numbers? Can you find the smallest number that lights up all four lights?

What happens when you turn these cogs? Investigate the differences between turning two cogs of different sizes and two cogs which are the same.

Can you sort these triangles into three different families and explain how you did it?

What shape is the overlap when you slide one of these shapes half way across another? Can you picture it in your head? Use the interactivity to check your visualisation.

This was a problem for our birthday website. Can you use four of these pieces to form a square? How about making a square with all five pieces?

Board Block game for two. Can you stop your partner from being able to make a shape on the board?

Seeing Squares game for an adult and child. Can you come up with a way of always winning this game?

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?

Create a pattern on the left-hand grid. How could you extend your pattern on the right-hand grid?

What does the overlap of these two shapes look like? Try picturing it in your head and then use the interactivity to test your prediction.

There are three versions of this challenge. The idea is to change the colour of all the spots on the grid. Can you do it in fewer throws of the dice?

Sort the houses in my street into different groups. Can you do it in any other ways?

Place six toy ladybirds into the box so that there are two ladybirds in every column and every row.

The computer has made a rectangle and will tell you the number of spots it uses in total. Can you find out where the rectangle is?

Choose 13 spots on the grid. Can you work out the scoring system? What is the maximum possible score?

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

What happens when you try and fit the triomino pieces into these two grids?