Addition and subtraction

problem
Favourite

Impossibilities

Age

11 to 14

Challenge level

2 out of 3

Just because a problem is impossible doesn't mean it's difficult...
problem
Favourite

Cunning Card Trick

Age

11 to 14

Challenge level

3 out of 3

Delight your friends with this cunning trick! Can you explain how it works?
problem
Favourite

Consecutive Negative Numbers

Age

11 to 14

Challenge level

3 out of 3

Do you notice anything about the solutions when you add and/or subtract consecutive negative numbers?
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Favourite

Connect Three

Age

11 to 16

Challenge level

2 out of 3

In this game the winner is the first to complete a row of three. Are some squares easier to land on than others?
problem

Double Digit

Age

11 to 14

Challenge level

1 out of 3

Choose two digits and arrange them to make two double-digit numbers. Now add your double-digit numbers. Now add your single digit numbers. Divide your double-digit answer by your single-digit answer. Try lots of examples. What happens? Can you explain it?
problem

Alphabet Soup

Age

11 to 14

Challenge level

1 out of 3

This challenge is to make up YOUR OWN alphanumeric. Each letter represents a digit and where the same letter appears more than once it must represent the same digit each time.
problem

As Easy as 1,2,3

Age

11 to 14

Challenge level

1 out of 3

When I type a sequence of letters my calculator gives the product of all the numbers in the corresponding memories. What numbers should I store so that when I type 'ONE' it returns 1, and when I type 'TWO' it returns 2, and so on.
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Kids

Age

11 to 14

Challenge level

1 out of 3

Find the numbers in this sum
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Machines

Age

7 to 11

Challenge level

1 out of 3

What is happening at each box in these machines?
problem

Card Trick 2

Age

11 to 14

Challenge level

2 out of 3

Can you explain how this card trick works?