Odd and even numbers

problem

Neighbourly addition

Age

7 to 14

Challenge level

I added together some of my neighbours' house numbers. Can you explain the patterns I noticed?
problem

Magic crosses

Age

7 to 14

Challenge level

Can you find examples of magic crosses? Can you find all the possibilities?
$What Could \It Be?$

problem
Favourite

What could it be?

Age

5 to 7

Challenge level

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

Play to 37

Age

7 to 11

Challenge level

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.
problem
Favourite

Sorting the numbers

Age

7 to 11

Challenge level

Can you put the numbers in the correct place in this Carroll diagram?
problem
Favourite

Square subtraction

Age

7 to 11

Challenge level

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?
problem
Favourite

Take three numbers

Age

7 to 11

Challenge level

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

Odd times even

Age

5 to 7

Challenge level

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

Two numbers under the microscope

Age

5 to 7

Challenge level

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

Magic letters

Age

11 to 14

Challenge level

Charlie has made a Magic V. Can you use his example to make some more? And how about Magic Ls, Ns and Ws?