Odd and even numbers

problem
What do you need?

Age

7 to 11

Challenge level

Four of these clues are needed to find the chosen number on this grid and four are true but do nothing to help in finding the number. Can you sort out the clues and find the number?
problem
Numbers as shapes

Age

5 to 7

Challenge level

Use cubes to continue making the numbers from 7 to 20. Are they sticks, rectangles or squares?
problem
Domino sorting

Age

5 to 7

Challenge level

Try grouping the dominoes in the ways described. Are there any left over each time? Can you explain why?
problem
Seven flipped

Age

7 to 11

Challenge level

Investigate the smallest number of moves it takes to turn these mats upside-down if you can only turn exactly three at a time.
problem
Domino pick

Age

5 to 7

Challenge level

Are these domino games fair? Can you explain why or why not?
problem
Odds and evens

Age

11 to 14

Challenge level

Are these games fair? How can you tell?
problem
Crossings

Age

7 to 11

Challenge level

In this problem we are looking at sets of parallel sticks that cross each other. What is the least number of crossings you can make? And the greatest?
problem
Number differences

Age

7 to 11

Challenge level

Place the numbers from 1 to 9 in the squares below so that the difference between joined squares is odd. How many different ways can you do this?
problem
More numbers in the ring

Age

5 to 7

Challenge level

If there are 3 squares in the ring, can you place three different numbers in them so that their differences are odd? Try with different numbers of squares around the ring. What do you notice?
problem
Ring a ring of numbers

Age

5 to 7

Challenge level

Choose four of the numbers from 1 to 9 to put in the squares so that the differences between joined squares are odd.