What happens to the perimeter of triangle ABC as the two smaller circles change size and roll around inside the bigger circle?

A introduction to how patterns can be deceiving, and what is and is not a proof.

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.

Pick a square within a multiplication square and add the numbers on each diagonal. What do you notice?

Think of a two digit number, reverse the digits, and add the numbers together. Something special happens...

Four rods of equal length are hinged at their endpoints to form a rhombus. The diagonals meet at X. One edge is fixed, the opposite edge is allowed to move in the plane. Describe the locus of. . . .

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

Charlie has created a mapping. Can you figure out what it does? What questions does it prompt you to ask?

Do you notice anything about the solutions when you add and/or subtract consecutive negative numbers?

Helen made the conjecture that "every multiple of six has more factors than the two numbers either side of it". Is this conjecture true?

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. . . .

Take any whole number between 1 and 999, add the squares of the digits to get a new number. Make some conjectures about what happens in general.

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

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

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

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

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.

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

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?

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

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

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

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?

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?

If you'd like to know more about Primary Maths Masterclasses, this is the package to read! Find out about current groups in your region or how to set up your own.

Explore the relationship between simple linear functions and their graphs.

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.

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?