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?

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?

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

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?

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

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?

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

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?

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

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?

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

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?

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

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?

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

Surprise your friends with this magic square trick.

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

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

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

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

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

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

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

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.

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

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

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

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

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

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

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.

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 when you round these numbers to the nearest whole number?

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?

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

Jo has three numbers which she adds together in pairs. When she does this she has three different totals: 11, 17 and 22 What are the three numbers Jo had to start with?”

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

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

Choose any 3 digits and make a 6 digit number by repeating the 3 digits in the same order (e.g. 594594). Explain why whatever digits you choose the number will always be divisible by 7, 11 and 13.

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?

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?

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

Investigate the different ways that fifteen schools could have given money in a charity fundraiser.

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?

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

Investigate the sum of the numbers on the top and bottom faces of a line of three dice. What do you notice?

Is there an efficient way to work out how many factors a large number has?

Are these statements relating to odd and even numbers always true, sometimes true or never true?

This article for primary teachers discusses how we can help learners generalise and prove, using NRICH tasks as examples.