Addition and subtraction

problem
Make 100

Age

7 to 11

Challenge level

Find at least one way to put in some operation signs to make these digits come to 100.
problem
Abundant numbers

Age

7 to 11

Challenge level

48 is called an abundant number because it is less than the sum of its factors (without itself). Can you find some more abundant numbers?
problem
Zios and Zepts

Age

7 to 11

Challenge level

On the planet Vuv there are two sorts of creatures. The Zios have 3 legs and the Zepts have 7 legs. The great planetary explorer Nico counted 52 legs. How many Zios and how many Zepts were there?
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
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
What's in a name?

Age

5 to 7

Challenge level

What do you notice about these squares of numbers? What is the same? What is different?
problem
Clever keys

Age

7 to 11

Challenge level

On a calculator, make 15 by using only the 2 key and any of the four operations keys. How many ways can you find to do it?
problem
Pouring the punch drink

Age

7 to 11

Challenge level

There are 4 jugs which hold 9 litres, 7 litres, 4 litres and 2 litres. Find a way to pour 9 litres of drink from one jug to another until you are left with exactly 3 litres in three of the jugs.
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
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?