Working systematically

Trinni rearranges numbers on a clock face so each adjacent pair add up to a triangle number... What number did she put where 6 would usually be?

The sum of each column and row in this grid give the totals as shown. What number goes in the starred square?

Can you picture how to order the cards to reproduce Charlie's card trick for yourself?

You have been given nine weights, one of which is slightly heavier than the rest. Can you work out which weight is heavier in just two weighings of the balance?

Rather than using the numbers 1-9, this sudoku uses the nine different letters used to make the words "Advent Calendar".

An extra constraint means this Sudoku requires you to think in diagonals as well as horizontal and vertical lines and boxes of nine.

Can you solve this magic square?

In how many ways can you give change for a ten pence piece?

You need to find the values of the stars before you can apply normal Sudoku rules.

What is the smallest number of ferry trips that Neda needs to take to visit all four islands and return to the mainland?