Sudoku for Kids - Page 2

Did you figure out that R4C7 has to be a 4? If you did, give yourself a pat on the back!

Since possibilities 1,2,3,5,6,7,8 and 9 were taken by other squares in row 4, column 7 and block 6, R4C7 has to be a 4! This is called a force because R4C7 is forced to be a 4.

So go and put a big 4 in R4C7! You’ve solved a square. Here’s what your puzzle should look like now:

Sudoku puzzle

You should have the 1,5,8 possibilities in R1C1, and 4 in R4C7.

Now lets consider square R5C8. That’s the square right in the middle of block 6.

What possibilities can it have? If you answered 3 and 8, you’re right. Pencil them in!

Sudoku puzzle

Well, you didn’t solve a square, but you did learn something. Oh well, let’s try another square. What about R4C8, the square right above it? What possibilities does it have?

If you answered, “Hey, R4C8 has to be an 8!”, you’re right! Fill it in!

And did you notice something else? Remember R5C8, the square right below that had to be a 3 or an 8. Well, if R4C8 has to be an 8, then R5C8 can’t be an 8 (duh!)

So you can scratch out the little 8 you penciled into R5C8. This is called removing a possibility. (double-duh!). In fact, you can scratch out 8 in any square in row 5, column 8 and block 6, but since we haven’t figured out those possibilities yet, you don’t have to.

So what’s left in R5C8? We knew it had to be a 3 or an 8, and now we know it can’t be an 8. So it must be a 3! (triple-duh!). So fill it in. Now look at R6C7. It’s the only square in block 6 that we haven’t filled in. So (double-double-duh!) it can only have one possibility. What number is left? Easy huh? It has to be a 1!
So we can fill in block 6 like this:

Sudoku puzzle

Look carefully at this puzzle and you’ll see something horrible! Awful! Terrible!

All of the squares have two or more possibilities! There are no forced squares! But if you look carefully at row 1, and in particular square R1C5, you’ll see something interesting. What’s special about R1C5?

Did you figure out that R1C5 must be a 9? If you did, congratulations, you’ve found your first pin!

What’s that? You didn’t get it? Okay, let me explain.

Look carefully at all the squares in row 1. Check out their possibilities. R1C5 is the only square that has 9 as a possibility! Since none of the other blank squares can be a 9, R1C5 must be the 9!

When a square is the only square in a row, column or block than can contain a certain number, we say it is pinned to that number.

You’ll need to find two other pins in the puzzle to solve it. Hint: they are all in rows.

Pretty cool, eh? You can test your pin perception prowess with the puzzle on the next page. It is filled with pins, in rows, columns and even blocks!

While you are doing it, think of ways to make it easier to find pins. Can you come up with a good way of doing it quickly? If you are learning to Sudoku with some friends or in a class, why not tell each other how you do it. Maybe someone will come up with a really good method.

PS: Don’t you hate it when your teacher gives you “busywork?” Me too. So no “pencilling in the possibilities” busywork for you! All the rest of the puzzles in this tutorial will have the possibilities filled in.

The Pin Perception Prowess Puzzle!

Sudoku puzzle

 

Lesson 3 - Locking In Progress

Sudoku puzzle

Time to really put on your thinking caps, kids! At this point, the puzzle has no forces and no pins! How can you possibly make progress?

Look carefully at row 2. Is there anything special about the blank squares? Anything you can use to make some progress?

This is a toughie, so don’t be too hard on yourself if you don’t get it!

Okay, if you figured out that R2C1 and R2C9 can’t contain a 2 or a 3, go to the head of the class! In fact, tell Mom and Dad you deserve extra dessert tonight!

Here’s how it works: Look at R2C5 and R2C6. Both of these squares have possibilities 2 and 3. This lets us make an important logical deduction.

Think about it. If R2C5 is a 2, then R2C6 will be forced to be an 3. And if R2C5 is an 3, then R2C6 will be forced to be a 2.

Either way, one of them will be the 2 in row 2, and the other will be the 3. And that means no other square in row 2 can be a 2 or a 3! Possibilities 2 and 3 have been locked into R2C5 and R2C6, thus we call them a simple locked pair of squares. There are sneakier versions of locked pairs you’ll learn later, which is why these are called “simple” locked pairs.

Extra credit: Did you notice that R2C5 and R2C6 are also a simple locked pair in block 2? They just happen to be both in row 2 and block 2. So you can not only remove 2 and 3 as possibilities from R2C1 and R2C9, but also R3C4, R3C5 and R3C6!

Note that after removing 2 and 3 from R3C4 and R3C5, they become a new locked pair. However, this doesn’t help you because it doesn’t let you remove any possibilities. Not every locked pair is useful, but enough are that you should definitely keep an eye out for them. Good thing they are easy to see!

You’ll need to find at least one more locked pair, and a lot of forces and pins, in order to solve the puzzle. Good luck!

Homework: Let’s say you find a row that has three empty squares, all with possibilities 1, 2 and 3. Could this help you remove possibilities from other squares in the row? Here’s some space to write down your answer:

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Homework answers next page

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