This challenge focuses on finding the sum and difference of pairs of two-digit numbers.

This challenge is about finding the difference between numbers which have the same tens digit.

This task follows on from Build it Up and takes the ideas into three dimensions!

Find the sum and difference between a pair of two-digit numbers. Now find the sum and difference between the sum and difference! What happens?

Two children made up a game as they walked along the garden paths. Can you find out their scores? Can you find some paths of your own?

Tom and Ben visited Numberland. Use the maps to work out the number of points each of their routes scores.

Try adding together the dates of all the days in one week. Now multiply the first date by 7 and add 21. Can you explain what happens?

Can you make dice stairs using the rules stated? How do you know you have all the possible stairs?

How can you arrange these 10 matches in four piles so that when you move one match from three of the piles into the fourth, you end up with the same arrangement?

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

Put the numbers 1, 2, 3, 4, 5, 6 into the squares so that the numbers on each circle add up to the same amount. Can you find the rule for giving another set of six numbers?

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

Frances and Rishi were given a bag of lollies. They shared them out evenly and had one left over. How many lollies could there have been in the bag?

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

In a Magic Square all the rows, columns and diagonals add to the 'Magic Constant'. How would you change the magic constant of this square?

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

We can arrange dots in a similar way to the 5 on a dice and they usually sit quite well into a rectangular shape. How many altogether in this 3 by 5? What happens for other sizes?

This challenge, written for the Young Mathematicians' Award, invites you to explore 'centred squares'.

This challenge encourages you to explore dividing a three-digit number by a single-digit number.

Use your addition and subtraction skills, combined with some strategic thinking, to beat your partner at this game.

Benâ€™s class were cutting up number tracks. First they cut them into twos and added up the numbers on each piece. What patterns could they see?

In this calculation, the box represents a missing digit. What could the digit be? What would the solution be in each case?

Strike it Out game for an adult and child. Can you stop your partner from being able to go?

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

These squares have been made from Cuisenaire rods. Can you describe the pattern? What would the next square look like?

What can you say about these shapes? This problem challenges you to create shapes with different areas and perimeters.

In each of the pictures the invitation is for you to: Count what you see. Identify how you think the pattern would continue.

What happens if you join every second point on this circle? How about every third point? Try with different steps and see if you can predict what will happen.

Watch this animation. What do you notice? What happens when you try more or fewer cubes in a bundle?

Polygonal numbers are those that are arranged in shapes as they enlarge. Explore the polygonal numbers drawn here.

Can you dissect an equilateral triangle into 6 smaller ones? What number of smaller equilateral triangles is it NOT possible to dissect a larger equilateral triangle into?

Find the sum of all three-digit numbers each of whose digits is odd.

Try out this number trick. What happens with different starting numbers? What do you notice?

Can you continue this pattern of triangles and begin to predict how many sticks are used for each new "layer"?

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

An investigation that gives you the opportunity to make and justify predictions.

While we were sorting some papers we found 3 strange sheets which seemed to come from small books but there were page numbers at the foot of each page. Did the pages come from the same book?

Does this 'trick' for calculating multiples of 11 always work? Why or why not?

Use two dice to generate two numbers with one decimal place. What happens when you round these numbers to the nearest whole number?

What happens when you round these three-digit numbers to the nearest 100?

Can you put the numbers 1-5 in the V shape so that both 'arms' have the same total?

What happens when you round these numbers to the nearest whole number?

Here are some arrangements of circles. How many circles would I need to make the next size up for each? Can you create your own arrangement and investigate the number of circles it needs?

Use the interactivity to investigate what kinds of triangles can be drawn on peg boards with different numbers of pegs.

Compare the numbers of particular tiles in one or all of these three designs, inspired by the floor tiles of a church in Cambridge.

How many different journeys could you make if you were going to visit four stations in this network? How about if there were five stations? Can you predict the number of journeys for seven stations?

Watch this animation. What do you see? Can you explain why this happens?

Take a counter and surround it by a ring of other counters that MUST touch two others. How many are needed?

Can you find a way of counting the spheres in these arrangements?