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?

Try to stop your opponent from being able to split the piles of counters into unequal numbers. Can you find a strategy?

Think of a number, square it and subtract your starting number. Is the number you’re left with odd or even? How do the images help to explain this?

If there are 3 squares in the ring, can you place three different numbers in them so that their differences are odd? Try with different numbers of squares around the ring. What do you notice?

Use the interactivities to complete these Venn diagrams.

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

Use the interactivity to sort these numbers into sets. Can you give each set a name?

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....?

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

Yasmin and Zach have some bears to share. Which numbers of bears can they share so that there are none left over?

Can you order the digits from 1-3 to make a number which is divisible by 3 so when the last digit is removed it becomes a 2-figure number divisible by 2, and so on?

Can you find the chosen number from the grid using the clues?

Mr Gilderdale is playing a game with his class. What rule might he have chosen? How would you test your idea?

This article introduces the idea of generic proof for younger children and illustrates how one example can offer a proof of a general result through unpacking its underlying structure.

Choose four of the numbers from 1 to 9 to put in the squares so that the differences between joined squares are odd.

Daisy and Akram were making number patterns. Daisy was using beads that looked like flowers and Akram was using cube bricks. First they were counting in twos.

Arrange the numbers 1 to 6 in each set of circles below. The sum of each side of the triangle should equal the number in its centre.

This problem challenges you to find out how many odd numbers there are between pairs of numbers. Can you find a pair of numbers that has four odds between them?

You can trace over all of the diagonals of a pentagon without lifting your pencil and without going over any more than once. Can the same thing be done with a hexagon or with a heptagon?

Place the numbers from 1 to 9 in the squares below so that the difference between joined squares is odd. How many different ways can you do this?

Pat counts her sweets in different groups and both times she has some left over. How many sweets could she have had?

Use cubes to continue making the numbers from 7 to 20. Are they sticks, rectangles or squares?

How many different sets of numbers with at least four members can you find in the numbers in this box?

There is a clock-face where the numbers have become all mixed up. Can you find out where all the numbers have got to from these ten statements?

A game for 2 or more people. Starting with 100, subratct a number from 1 to 9 from the total. You score for making an odd number, a number ending in 0 or a multiple of 6.

Try grouping the dominoes in the ways described. Are there any left over each time? Can you explain why?

How would you create the largest possible two-digit even number from the digit I've given you and one of your choice?

If you have ten counters numbered 1 to 10, how many can you put into pairs that add to 10? Which ones do you have to leave out? Why?

There are ten children in Becky's group. Can you find a set of numbers for each of them? Are there any other sets?

I am less than 25. My ones digit is twice my tens digit. My digits add up to an even number.

How many legs do each of these creatures have? How many pairs is that?

This investigates one particular property of number by looking closely at an example of adding two odd numbers together.

In this game for two players, the idea is to take it in turns to choose 1, 3, 5 or 7. The winner is the first to make the total 37.

What happens when you add three numbers together? Will your answer be odd or even? How do you know?

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

This problem looks at how one example of your choice can show something about the general structure of multiplication.

Look at what happens when you take a number, square it and subtract your answer. What kind of number do you get? Can you prove it?

Four bags contain a large number of 1s, 3s, 5s and 7s. Pick any ten numbers from the bags above so that their total is 37.

In this problem we are looking at sets of parallel sticks that cross each other. What is the least number of crossings you can make? And the greatest?

How have the numbers been placed in this Carroll diagram? Which labels would you put on each row and column?

Four of these clues are needed to find the chosen number on this grid and four are true but do nothing to help in finding the number. Can you sort out the clues and find the number?

This article for teachers describes how number arrays can be a useful reprentation for many number concepts.

In how many different ways can you break up a stick of 7 interlocking cubes? Now try with a stick of 8 cubes and a stick of 6 cubes.

Use the interactivities to fill in these Carroll diagrams. How do you know where to place the numbers?