Reasoning, convincing and proving

problem
Air nets

Age

7 to 18

Challenge level

Can you visualise whether these nets fold up into 3D shapes? Watch the videos each time to see if you were correct.
problem
Treasure hunt

Age

7 to 14

Challenge level

Can you find a reliable strategy for choosing coordinates that will locate the treasure in the minimum number of guesses?
problem
Magic Vs

Age

7 to 11

Challenge level

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

Age

11 to 14

Challenge level

Crosses can be drawn on number grids of various sizes. What do you notice when you add opposite ends?
problem
Out of line

Age

11 to 14

Challenge level

Fill in the grid with A-E like a Sudoku. Which letter is in the starred square?
problem
Quiz questions

Age

11 to 14

Challenge level

Jack does a 20-question quiz. How many questions didn't he attempt?
problem
Distinct in a line

Age

11 to 14

Challenge level

This grid can be filled so that each of the numbers 1, 2, 3, 4, 5 appears just once in each row, column and diagonal. Which number goes in the centre square?
problem
Stats statements

Age

16 to 18

Challenge level

Are these statistical statements sometimes, always or never true? Or it is impossible to say?
problem
Thousands and millions

Age

11 to 14

Challenge level

Here's a chance to work with large numbers...
problem
LCM Sudoku

Age

14 to 16

Challenge level

Here is a Sudoku with a difference! Use information about lowest common multiples to help you solve it.