Variant Sudoku Trivia Game | Brain Teasers

Quiz Answer Key and Fun Facts

1. German whispers is an extra constraint that can be placed on a sudoku grid which adds a green line connecting some the squares. The adjacent digits along that line must all differ by at least 5. Which digit can never appear on the green line?

Answer: 5

A 5 can never be placed on a German whisper line because there is no sudoku digit that differs from 5 by more than 5 (0 and 10 are not sudoku digits). The German whisper rule also restricts a 4 to a neighbor of 9, and a 6 to a neighbor of 1.

2. A Magic Square is one in which all rows, columns and diagonals add up to the same number. If the central 3x3 square of a sudoku grid must be a magic square, what number is the magic square sum?

Answer: 15

To determine what the row/column/diagonal sum must be, consider that the digits 1-9 add up to 45. Since there are three columns, each column must add up to 15, and the same is true for the three rows. If this is to be the case, the digit 5 must be in the centre square of these 9, with the others placed so that pairs that add to 10 are on opposite sides of the centre from each other.

This can be done either by placing the even digits in the four corners appropriately, then the odd digits in the non-corner squares, or the reverse.

3. A killer cage is a dashed line incorporating a number of adjacent cells, with a small digit written in the top left corner. All numbers within a cage must sum to the digit in the top left corner of the cage. Which two-digit killer sum cage is impossible?

Answer: 19

The only way to reach a killer cage with a sum of 19 is to add two numbers where one is necessarily greater than 9. Since 9 is the largest sudoku digit available, a killer cage of 19 or more is not possible. Killer cages can be very effective in restricting digits. For instance, a killer cage adding to 3 must necessarily include a 1 and a 2.

4. Killer Cages: All numbers within a cage must add up to the digit in the top left corner of the cage. A two-cell cage adds up to 11. Which number cannot be included in such a cage?

Answer: 1

A 1 can never be in a two-cell 11 cage, because that would immediately imply that its partner would be a 10, which is not a standard sudoku digit. There are four combinations of sudoku digits that can add to 11 (2-9, 3-8, 4-7, and 5-6).

5. A Renban line is a pink line connecting a number of adjacent squares. All digits on a pink Renban line are a set of non-repeating, consecutive digits in any order. Which of the following digits MUST be on a 6-cell Renban line?

Answer: 4,5, and 6

The smallest possible 6-cell consecutive combination would be from 1 to 6. The largest possible 6-cell consecutive combination would be from 4 to 9. Therefore, the digits 4, 5, and 6 must necessarily be included in a 6-cell Renban. A 5 is the only necessary number required to complete a 5-cell Renban.

6. You are told that a sudoku grid has a grey line connecting cells which are to form a palindrome line. What is a palindrome line?

Answer: They read the same backwards and forwards

Palindrome lines, as the word implies, must read the same way backwards and forwards, similarly to palindromes, that are words that are written the same way in both directions. An example would be "Hannah". Palindrome lines are a setter's best friend in variant sudoku, because finding one number on a palindrome line translates to two revealed digits for the solver.

For example, in a three-cell palindrome line, finding one digit on the edge of the line will automatically allow the solver to find a digit located on the other edge.

7. In a sudoku grid with a knight's move constraint, all squares that are a knight's move away from each other cannot contain the same digit. The "knight's move" is borrowed from chess and is an "L" shaped move of either two squares vertically and one horizontally, or two squares horizontally and one vertically. How many knight's moves can the central square reach?

Answer: 8

Chess famously employs the horse shaped knight, which always moves in an "L" formation - either two squares vertically and one horizontally, or two squares horizontally and one vertically. Sudoku with knight's move constraints can be incredibly rewarding to solve because one has to constantly remind themselves to check all possible knight's moves, which can enhance the puzzle's flow and internal logic.

The central square, and in fact, most other squares in the puzzle, can reach up to 8 different squares by "knight's move".

This is identical to chess, and is the reason the knight is considered to be at its most powerful at the center of the board, and at its weakest on the edges, where it has significantly lower reach.

8. An important feature of variant sudoku is often summation and math related. All numbers 1-9 add up to 45, and this is an important number to remember when solving variant sudoku. What is the term for the sum of consecutive whole numbers (starting with 1)?

Answer: Triangular Number

The triangular number of 9 is 45. The smallest triangular number is 1. The terminology comes from placing 1 dot, then 2 underneath it, then 3 underneath that, until you reach your desired total. This visually resembles a triangle. Knowing the triangular number for 9, and indeed for all the other sudoku digits, is crucial when solving some of those brutal math problems disguised as sudoku :)

9. A Kropki dot is a small, white circle that connects two cells together. All digits on a Kropki dot must be in a 1:2 or 2:1 ratio with each other. Which of the following digits cannot be placed on these dots?

Answer: 7

The numbers 5, 7, and 9 cannot be placed on Kropki dots because (as odd numbers) they cannot be halved to create an integer, and they cannot be doubled because their double is too large to be a single sudoku digit. 1 and 3 are the only odd numbers that can be placed on Kropki dots because they can double to 2 and 6 respectively, which are Sudoku digits.

10. A thermometer is a large grey circle (representing a bulb) with a grey line protruding from said bulb. Digits in a thermometer must strictly increase from bulb to tip (not unlike a real thermometer). You see a 6-cell thermometer. Which number cannot be in the bulb?

Answer: 5

The number of digits necessarily greater than the bulb in a 6-cell thermometer is 5. If a 5 was to be placed in the bulb, then even without skipping a single number, the tip of the thermometer would reach 10, which is not a sudoku digit.

Source: Author dim_dude

This quiz was reviewed by FunTrivia editor Fifiona81 before going online.
Any errors found in FunTrivia content are routinely corrected through our feedback system.

Variant Sudoku Trivia Quiz

Many are familiar with sudoku, where a 9x9 grid is filled with the digits 1 to 9. Here are some of the rules that make the game much more interesting, and in some cases, set up grids that require no given digits to solve. Enjoy :)

NEXT>

NEXT>

NEXT>

NEXT>

NEXT>

NEXT>

NEXT>

NEXT>

NEXT>