This big box adds something to any number that goes into it. If you know the numbers that come out, what addition might be going on in the box?

Proof does have a place in Primary mathematics classrooms, we just need to be clear about what we mean by proof at this level.

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

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?

Are these statements always true, sometimes true or never true?

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

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

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

Here are two kinds of spirals for you to explore. What do you notice?

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

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

Look at three 'next door neighbours' amongst the counting numbers. Add them together. What do you notice?

Are these statements relating to calculation and properties of shapes always true, sometimes true or never true?

Watch this video to see how to roll the dice. Now it's your turn! What do you notice about the dice numbers you have recorded?

This task combines spatial awareness with addition and multiplication.

This task, written for the National Young Mathematicians' Award 2016, focuses on 'open squares'. What would the next five open squares look like?

This challenge combines addition, multiplication, perseverance and even proof.

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.

This ladybird is taking a walk round a triangle. Can you see how much he has turned when he gets back to where he started?

In sheep talk the only letters used are B and A. A sequence of words is formed by following certain rules. What do you notice when you count the letters in each word?

This article for teachers discusses examples of problems in which there is no obvious method but in which children can be encouraged to think deeply about the context and extend their ability to. . . .

Find out about Magic Squares in this article written for students. Why are they magic?!

Becky created a number plumber which multiplies by 5 and subtracts 4. What do you notice about the numbers that it produces? Can you explain your findings?

Problem solving is at the heart of the NRICH site. All the problems give learners opportunities to learn, develop or use mathematical concepts and skills. Read here for more information.

Use the information about the ducks on a particular farm to find out which of the statements about them must be true.

Is it possible to draw a 5-pointed star without taking your pencil off the paper? Is it possible to draw a 6-pointed star in the same way without taking your pen off?

Investigate and explain the patterns that you see from recording just the units digits of numbers in the times tables.

For this task, you'll need an A4 sheet and two A5 transparent sheets. Decide on a way of arranging the A5 sheets on top of the A4 sheet and explore ...

Explore Alex's number plumber. What questions would you like to ask? Don't forget to keep visiting NRICH projects site for the latest developments and questions.

Are these statements always true, sometimes true or never true?