Sunday, June 26, 2022

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Home Series Sudoku for Dummies Sudoku for Dummies – Level 2

Sudoku for Dummies – Level 2

Sudoku for Dummies – Level 2

Congratulations to Hector Juarez ’19 for completing last week’s boss level. If you have any questions, feel free to email him at




Now that we’ve got the basics down (click here for Level 1), it’s time to take things to the next level! Literally – check the title…

Let us begin!

Lesson 2.1

As the puzzles get harder, we need a way to organize our thoughts and observations. Sure, with Boss Level 1, you could probably get away with a few mental calculations.

But this is not Level 1.

This is Level 2! And now it’s time for us to step up our Sudoku game and start notating.

So here is Boss Level 1 notated. (Sorry for the different look, I couldn’t find the old website.)

As you can see, the notes are very organized. Each number has its own mini-box, which makes it very easy to look through and find certain numbers.

Your notes must be organized, if they aren’t you might as well not notate at all because it’ll be a mess.

As you can see from the notes, three squares (two on the bottom, one on the right) only have one candidate (a candidate is a number that could possibly go in the box).

Since this was Level 1, notation was a bit overkill. But pretty soon there won’t be any super-obvious answers like these. Notating is a way to keep track of your deductions. Without it, higher level puzzles are impossible (unless you are a computer or a Jedi master).

Lesson 2.2

Now that we’re all notated up, it’s time to make it useful.

As you can see, the puzzle is mostly filled in, but none of the squares have an apparent answer…

It’s time to make use of a great trick called the Naked Pair.

Take a look at the fourth column. Two of the squares can only be a 1 or an 8.

Think about that. What if the top box of the fourth column has a 1? What if it has an 8?

If Row 1 Column 4 is a 1, then Row 8 Column 4 has to be an 8. Take a minute and look at the puzzle if that doesn’t make sense.

That means that no 1s or 8s are possible in the rest of the column. Take a look:


Remember these were just hypothetical. There were only 2 candidates in each square, so each of these shows the 2 possibilities. It’s impossible to know which one is correct right now, but what they have in common must be true.

As you can see, I put an X through all the candidates that can’t be true under this assumption, and the same for the one below.





Since we’ve gone through 100% of the possibilities for these two boxes, the common Xs must be true no matter what.




So, the circled ones can’t be true no matter what, and you can erase them.

Keep in mind, 2.2 also applies when the Naked Pair is in the same box.

Lesson 2.3

The last strategy we’ll look at today is the locked candidate. This means the candidates in a certain big box can only go in one row or column. Lets take a look:

Let’s check out rows 4 and 5, column 3. Both have 9s. Why is this useful you ask? Those two 9s are the only 9s in the big box!

What’s the rule about big boxes, rows, and columns? Exactly one of each number 1-9.

Since a 9 has to be in the big box, but all the candidates are in the same column. So if there is a 9 in column four, it has to be in the middle big-box (otherwise all the 9 candidates in that box would be eliminated).

Here you can see, the two 9s in green are the only ones in the big box. They are also in the same column, so the 9 in Row 9 Column 3 must be eliminated.

Now that that 9 (with an X through it) is gone, did anything useful pop out at you? Maybe from lesson 2.2? Check it out for a second.

If you saw that the leftover 2 and 8 was a naked pair with Row 2 Column 3 congratulations! How’s that for tying it all together!

If you had trouble seeing that, that’s OK. Sometimes I spend 10 minutes staring at a puzzle only to spot a super obvious trick I overlooked. Patience is super important with Sudoku! I hate to break it to, but it only gets harder, and you’ll have to keep your eyes peeled for all of these tricks.

If you had trouble understanding these lessons, please let me know. I made this series to simplify Sudoku tutorials, so if it isn’t simple enough, tell me!

Boss Level 2

Have fun solving this one my growing grasshoppers!

Again, first person to email me ( a correct solution will be featured in next week’s episode.

Happy Sudoku-ing, and see you next week on The Roundup!



P.S. I’m super excited to write next week! Section 3’s lessons are kind of why I started this series, because most explanations are pretty hard to understand. After Level 3 you’ll be able to do most any Sudoku! Damn you guys learn fast! – See ya Friday!