Arrange the four number cards on the grid, according to the rules, to make a diagonal, vertical or horizontal line.
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?
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?
Choose four of the numbers from 1 to 9 to put in the squares so that the differences between joined squares are odd.
Place the numbers 1 to 10 in the circles so that each number is the difference between the two numbers just below it.
This 100 square jigsaw is written in code. It starts with 1 and ends with 100. Can you build it up?
Investigate the smallest number of moves it takes to turn these mats upside-down if you can only turn exactly three at a time.
An odd version of tic tac toe
Ben and his mum are planting garlic. Use the interactivity to help you find out how many cloves of garlic they might have had.
Use the information about Sally and her brother to find out how many children there are in the Brown family.
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?
In your bank, you have three types of coins. The number of spots shows how much they are worth. Can you choose coins to exchange with the groups given to make the same total?
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....?
Move just three of the circles so that the triangle faces in the opposite direction.
Starting with the number 180, take away 9 again and again, joining up the dots as you go. Watch out - don't join all the dots!
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?
Can you work out how to balance this equaliser? You can put more than one weight on a hook.
Our 2008 Advent Calendar has a 'Making Maths' activity for every day in the run-up to Christmas.
Place the numbers 1 to 6 in the circles so that each number is the difference between the two numbers just below it.
Here is a chance to play a version of the classic Countdown Game.
Choose a symbol to put into the number sentence.
Have a go at this well-known challenge. Can you swap the frogs and toads in as few slides and jumps as possible?
Investigate which numbers make these lights come on. What is the smallest number you can find that lights up all the lights?
Twenty four games for the run-up to Christmas.
If you have only four weights, where could you place them in order to balance this equaliser?
How have the numbers been placed in this Carroll diagram? Which labels would you put on each row and column?
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?
Use the interactivities to fill in these Carroll diagrams. How do you know where to place the numbers?
How many trains can you make which are the same length as Matt's, using rods that are identical?
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 see why 2 by 2 could be 5? Can you predict what 2 by 10 will be?
A variant on the game Alquerque
Place six toy ladybirds into the box so that there are two ladybirds in every column and every row.
NRICH December 2006 advent calendar - a new tangram for each day in the run-up to Christmas.
Can you put the numbers 1 to 8 into the circles so that the four calculations are correct?
Can you find all the different triangles on these peg boards, and find their angles?
Complete the squares - but be warned some are trickier than they look!
Can you put the numbers from 1 to 15 on the circles so that no consecutive numbers lie anywhere along a continuous straight line?
Make one big triangle so the numbers that touch on the small triangles add to 10. You could use the interactivity to help you.
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?
Use the interactivity to help get a feel for this problem and to find out all the possible ways the balls could land.
Use the interactivity to sort these numbers into sets. Can you give each set a name?
Find out what a "fault-free" rectangle is and try to make some of your own.
This article gives you a few ideas for understanding the Got It! game and how you might find a winning strategy.
Use the interactivity to find out how many quarter turns the man must rotate through to look like each of the pictures.
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?
Can you use the numbers on the dice to reach your end of the number line before your partner beats you?
Can you find just the right bubbles to hold your number?
Can you find all the different ways of lining up these Cuisenaire rods?
How many different triangles can you make on a circular pegboard that has nine pegs?