Addition and subtraction

problem

Book Codes

Age

7 to 11

Challenge level

Look on the back of any modern book and you will find an ISBN code. Take this code and calculate this sum in the way shown. Can you see what the answers always have in common?
problem

Dodecamagic

Age

7 to 11

Challenge level

Here you see the front and back views of a dodecahedron. Each vertex has been numbered so that the numbers around each pentagonal face add up to 65. Can you find all the missing numbers?
problem

How Many Eggs?

Age

7 to 11

Challenge level

Peter, Melanie, Amil and Jack received a total of 38 chocolate eggs. Use the information to work out how many eggs each person had.
problem

Special 24

Age

7 to 11

Challenge level

Find another number that is one short of a square number and when you double it and add 1, the result is also a square number.
problem

Zargon Glasses

Age

7 to 11

Challenge level

Zumf makes spectacles for the residents of the planet Zargon, who have either 3 eyes or 4 eyes. How many lenses will Zumf need to make all the different orders for 9 families?
problem

Magic Circles

Age

7 to 11

Challenge level

Put the numbers 1, 2, 3, 4, 5, 6 into the squares so that the numbers on each circle add up to the same amount. Can you find the rule for giving another set of six numbers?
problem

Arranging the Tables

Age

7 to 11

Challenge level

There are 44 people coming to a dinner party. There are 15 square tables that seat 4 people. Find a way to seat the 44 people using all 15 tables, with no empty places.
problem

Number Juggle

Age

7 to 11

Challenge level

Fill in the missing numbers so that adding each pair of corner numbers gives you the number between them (in the box).
problem

A Rod and a Pole

Age

7 to 11

Challenge level

A lady has a steel rod and a wooden pole and she knows the length of each. How can she measure out an 8 unit piece of pole?
problem

Add 3 Dice

Age

7 to 11

Challenge level

Three dice are placed in a row. Find a way to turn each one so that the three numbers on top of the dice total the same as the three numbers on the front of the dice. Can you find all the ways to do this?