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Killer Sudoku by Sudoku.com
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# What is Killer Sudoku?

Killer Sudoku is a fun twist on the classic sudoku for those of you seeking something new and challenging. It’s also known by such names as sumdoku, addoku and sumoku puzzle but in a nutshell it’s pretty much the same number puzzle.

## What’s the difference between Sudoku and Killer Sudoku?

Although both number puzzles share a lot of similarities, there’s also a major difference – amount of arithmetics involved.

In Killer Sudoku there’s a new concept of a “cage” – a group of cells within a dotted line that make up a sum shown as a small number above. Like in Sudoku, your ultimate goal is to fill the grid with numbers, while paying attention to ”the sum rule”. Let’s review Killer Sudoku rules in detail below.

## How to play Killer Sudoku

• Fill all rows, columns, and 3x3 blocks with numbers 1-9 exactly like in classic sudoku.
• Pay attention to the cages – groups of cells indicated by dotted lines.
• Make sure the sum of numbers in each cage is equal to the number in the upper left corner of the cage.
• Numbers cannot repeat within cages, a single row, column, or 3x3 region.

### Are Killer Sudoku rules hard?

Although solving Killer Sudoku online seems a bit harder than classic sudoku, we made it accessible for players of all skill levels. This number puzzle comes with several difficulty levels – easy, medium, hard, and expert. This way, the number puzzles are great for both beginners and advanced Sudoku solvers. Daily Killer Sudoku practice makes perfect and we have no doubts you’ll become a master in no time!

### The best Killer Sudoku tactic

One of the best-kept secrets to solving Killer Sudoku is the so-called “45 rule”. As we know from the rules, each block, row or column shall contain all numbers from 1 to 9, making it 45 in total. By knowing this and subtracting the sums of cages we can reveal additional numbers. Let’s see this in action.

The sum of all numbers in the left column is equal to 45. We also see several cages in that column – 15, 9, 9 and 7. By subtracting them from 45 we’ll get the value of the bottom-left cell: 45 - 15 - 9 - 9 - 7 = 5. The sum of this cage is 14 and we can instantly fill in another cell – 14 - 5 = 9. This way, by applying the “45 rule” we filled two numbers on the empty grid and are off to a good start!

### Why you should play Killer Sudoku

Solving Killer Sudoku online has a lot of benefits. Daily Killer Sudoku sessions are said to help you train your brain, improve memory, concentration and logical thinking. If these practical reasons aren’t enough for you, Killer Sudoku is a fun time-killer too! Whether you’re waiting for plane boarding, stuck in a queue or just want to unplug from reality for a few minutes, Killer Sudoku should be your number puzzle of choice.