Addition and subtraction

problem
Diagonal sums

Age

7 to 14

Challenge level

In this 100 square, look at the green square which contains the numbers 2, 3, 12 and 13. What is the sum of the numbers that are diagonally opposite each other? What do you notice?
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
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.
problem
Function machines

Age

7 to 11

Challenge level

If the numbers 5, 7 and 4 go into this function machine, what numbers will come out?
problem
Carrying cards

Age

7 to 11

Challenge level

These sixteen children are standing in four lines of four, one behind the other. They are each holding a card with a number on it. Can you work out the missing numbers?
problem
Cuisenaire counting

Age

5 to 7

Challenge level

Here are some rods that are different colours. How could I make a yellow rod using white and red rods?
problem
Sheep talk

Age

7 to 11

Challenge level

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?
problem
Consecutive seven

Age

11 to 14

Challenge level

Can you arrange these numbers into 7 subsets, each of three numbers, so that when the numbers in each are added together, they make seven consecutive numbers?
problem
Twizzle's journey

Age

5 to 7

Challenge level

Twizzle, a female giraffe, needs transporting to another zoo. Which route will give the fastest journey?
problem
One million to seven

Age

7 to 11

Challenge level

Start by putting one million (1 000 000) into the display of your calculator. Can you reduce this to 7 using just the 7 key and add, subtract, multiply, divide and equals as many times as you like?