Counting

problem
Diagonal sums Sudoku

Age

7 to 16

Challenge level

Solve this Sudoku puzzle whose clues are in the form of sums of the numbers which should appear in diagonal opposite cells.
problem
Stone age counting

Age

5 to 7

Challenge level

What could these drawings, found in a cave in Spain, represent?
problem
Queue

Age

5 to 7

Challenge level

25 students are queuing in a straight line. How many are there between Julia and Jenny?
problem
Ladybird count

Age

5 to 7

Challenge level

Some children were playing a game. Make a graph or picture to show how many ladybirds each child had.
problem
Amazing card trick

Age

11 to 14

Challenge level

How is it possible to predict the card?
problem
1 to 8

Age

7 to 11

Challenge level

Place the numbers 1 to 8 in the circles so that no consecutive numbers are joined by a line.
problem
Voting paradox

Age

14 to 18

Challenge level

Some relationships are transitive, such as `if A>B and B>C then it follows that A>C', but some are not. In a voting system, if A beats B and B beats C should we expect A to beat C?
problem
Counting cards

Age

7 to 11

Challenge level

A magician took a suit of thirteen cards and held them in his hand face down. Every card he revealed had the same value as the one he had just finished spelling. How did this work?
problem
Ruler

Age

16 to 18

Challenge level

The interval 0 - 1 is marked into halves, quarters, eighths ... etc. Vertical lines are drawn at these points, heights depending on positions. What happens as this process goes on indefinitely?
problem
Which is quicker?

Age

7 to 11

Challenge level

Which is quicker, counting up to 30 in ones or counting up to 300 in tens? Why?