A particular technique for solving Sudoku puzzles, known as "naked pair", is explained in this easy-to-read article.
Can you use your powers of logic and deduction to work out the missing information in these sporty situations?
This Sudoku, based on differences. Using the one clue number can you find the solution?
This sudoku requires you to have "double vision" - two Sudoku's for the price of one
Four small numbers give the clue to the contents of the four surrounding cells.
Solve this Sudoku puzzle whose clues are in the form of sums of the numbers which should appear in diagonal opposite cells.
A Sudoku that uses transformations as supporting clues.
This Sudoku puzzle can be solved with the help of small clue-numbers on the border lines between pairs of neighbouring squares of the grid.
Problem solving is at the heart of the NRICH site. All the problems give learners opportunities to learn, develop or use mathematical concepts and skills. Read here for more information.
This Sudoku combines all four arithmetic operations.
You are given the Lowest Common Multiples of sets of digits. Find the digits and then solve the Sudoku.
This is a variation of sudoku which contains a set of special clue-numbers. Each set of 4 small digits stands for the numbers in the four cells of the grid adjacent to this set.
This article for teachers describes several games, found on the site, all of which have a related structure that can be used to develop the skills of strategic planning.
Four numbers on an intersection that need to be placed in the surrounding cells. That is all you need to know to solve this sudoku.
The puzzle can be solved by finding the values of the unknown digits (all indicated by asterisks) in the squares of the $9\times9$ grid.
Can you put the 25 coloured tiles into the 5 x 5 square so that no column, no row and no diagonal line have tiles of the same colour in them?
Each of the main diagonals of this sudoku must contain the numbers 1 to 9 and each rectangle width the numbers 1 to 4.
Can you use the information to find out which cards I have used?
Can you order pictures of the development of a frog from frogspawn and of a bean seed growing into a plant?
The challenge is to find the values of the variables if you are to solve this Sudoku.
In this article, the NRICH team describe the process of selecting solutions for publication on the site.
Try out the lottery that is played in a far-away land. What is the chance of winning?
A Sudoku with a twist.
In a square in which the houses are evenly spaced, numbers 3 and 10 are opposite each other. What is the smallest and what is the largest possible number of houses in the square?
Exactly 195 digits have been used to number the pages in a book. How many pages does the book have?
Can you find which shapes you need to put into the grid to make the totals at the end of each row and the bottom of each column?
In this Sudoku, there are three coloured "islands" in the 9x9 grid. Within each "island" EVERY group of nine cells that form a 3x3 square must contain the numbers 1 through 9.
This second Sudoku article discusses "Corresponding Sudokus" which are pairs of Sudokus with terms that can be matched using a substitution rule.
A Sudoku with clues as ratios or fractions.
When you throw two regular, six-faced dice you have more chance of getting one particular result than any other. What result would that be? Why is this?
A Latin square of order n is an array of n symbols in which each symbol occurs exactly once in each row and exactly once in each column.
Explore this how this program produces the sequences it does. What are you controlling when you change the values of the variables?
A magician took a suit of thirteen cards and held them in his hand face down. Every card he revealed had the same value as the one he had just finished spelling. How did this work?
Given the products of diagonally opposite cells - can you complete this Sudoku?
Roll two red dice and a green dice. Add the two numbers on the red dice and take away the number on the green. What are all the different possible answers?
A Sudoku with clues as ratios.
I was in my car when I noticed a line of four cars on the lane next to me with number plates starting and ending with J, K, L and M. What order were they in?
Rather than using the numbers 1-9, this sudoku uses the nine different letters used to make the words "Advent Calendar".
A cinema has 100 seats. Show how it is possible to sell exactly 100 tickets and take exactly £100 if the prices are £10 for adults, 50p for pensioners and 10p for children.
This pair of linked Sudokus matches letters with numbers and hides a seasonal greeting. Can you find it?
Find out about Magic Squares in this article written for students. Why are they magic?!
The puzzle can be solved with the help of small clue-numbers which are either placed on the border lines between selected pairs of neighbouring squares of the grid or placed after slash marks on. . . .
A few extra challenges set by some young NRICH members.
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?
Pentagram Pylons - can you elegantly recreate them? Or, the European flag in LOGO - what poses the greater problem?
A Sudoku with clues as ratios.
Place the numbers 1 to 8 in the circles so that no consecutive numbers are joined by a line.
60 pieces and a challenge. What can you make and how many of the pieces can you use creating skeleton polyhedra?
A Sudoku with a twist.
Two sudokus in one. Challenge yourself to make the necessary connections.