Working systematically

The digits 1-9 have been written in the squares so that each row and column sums to 13. What is the value of n?

How many ways are there of completing the mini-sudoku?

In a 7-digit numerical code, each group of four consecutive digits adds to 16, and each group of five consecutive digits adds to 19. What is the sum of all 7 digits?

Albert Einstein is experimenting with two unusual clocks. At what time do they next agree?

This activity investigates how you might make squares and pentominoes from Polydron.

How can you quickly sort a suit of cards in order from Ace to King?

Given a set of points (x,y) with distinct x values, find a polynomial that goes through all of them, then prove some results about the existence and uniqueness of these polynomials.

Can you use your powers of logic and deduction to work out the missing information in these sporty situations?

This tricky challenge asks you to find ways of going across rectangles, going through exactly ten squares.