Addition and subtraction

problem
Favourite

Amazing Card Trick

Age

11 to 14

Challenge level

How is it possible to predict the card?
problem
Favourite

Weights

Age

11 to 14

Challenge level

Different combinations of the weights available allow you to make different totals. Which totals can you make?
problem
Favourite

Impossibilities

Age

11 to 14

Challenge level

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

Consecutive Negative Numbers

Age

11 to 14

Challenge level

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

Connect Three

Age

11 to 16

Challenge level

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

Difference Sudoku

Age

14 to 16

Challenge level

Use the differences to find the solution to this Sudoku.
problem

Double Digit

Age

11 to 14

Challenge level

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

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

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.
problem

Kids

Age

11 to 14

Challenge level

Find the numbers in this sum