Sudoku for kids

Introduction

Sudoku is a number puzzle that you fill in a square grid.

What is a Grid?

A grid has rows and columns. This is a grid.

It has 4 rows and 4 columns.

Now see what happens when you change the size of this grid by sliding the blue button.

Unique Numbers

Now let’s say we have a grid with 2 rows and 2 columns. We can fill in numbers such that they do not repeat in rows or columns. We can only fill number 1 or 2.

Here is a grid that is incorrectly filled, because the first column has two 2s, and the second column has two 1s.

Try filling out this grid yourself. The numbers will turn red if you fill them incorrectly.

Let’s try one more, this time 3x3 (You can say this as “three-by-three”). In this grid you can only fill numbers 1, 2 or 3.

Boxes

When the grid size increases to 4x4 (“four-by-four”), there are now 4 “boxes”, each of 2 rows and 2 columns.

Solving this is a little harder as we also need to have unique numbers in each box.

This does not repeat numbers in rows and columns. It is still incorrect because Box 1 repeats the number 2.

Box 4 is correct because the number 1, 2, 3, 4 only appear once in every row, column and box.

Sudoku

The grid we have been playing with is the game of Sudoku. You win at Sudoku by filling in all the numbers while following the rules of the game. Those rules are:

1. Numbers cannot repeat in any row.
2. Numbers cannot repeat in any column.
3. Numbers cannot repeat in any box.

Try solving this puzzle.

Let’s play a game

We are now going to help you solve a 4x4 Sudoku.

Fill the blue coloured cell. Use the right arrow to move to next step and left arrow to go back.

Some things to try

Here are some ways to solve the next step in Sudoku. The idea is to figure out the one number that will go in a square without breaking any rules. We can do this by looking at rows, columns and boxes.

1. Pick a square. Make a list of which numbers are missing in the square’s row. For every number in the list, check if the number is already present in the square’s column. If it is, cross it out from the list. If only one number is left, that is what will go in the square. You can do the same by swapping rows and columns.
2. Pick a square. Make a list of which numbers are missing in the square’s box. Check if each of those numbers is already present in the square’s row or column. Cross out the ones that are present. If only one number is left in the list, that is the answer.
3. Pick 2 squares in the same row, column or box. Make a list of the missing numbers. Try out each number in each square and see if any of the rules are broken. Often, one of them will break some rule. That leaves the other number as the only correct choice for the square.
4. Generally, try to work on the row, column or box that has the least missing numbers (has most of the numbers already filled). This way, we only need to try a few numbers. If a row, column or box has only one missing number, you can easily fill it!

Now, let’s try to solve a 9X9 sudoku together. Remember, you can move your mouse over the squares to help you see the row, column and box for the square!

Hint

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You can play more Sudoku on Sudoku.com.

If you enjoyed this tutorial (or feel something can be improved), let us know.