Hidden One

One of the numbers in the square is hiding in plain sight.

Object of the Game

Find the one number in the square grid that when calculated with any two adjacent numbers cannot satisfy the given Equa. That is the hidden number.

How to Play

  • Select a grid size ranging in size from 2×3 to 6×6.
  • Calculate ALL three adjacent number combinations that satisfy the given Equa until you find the one that doesn’t.
  • A number used in one combination, can be used in another.
  • Numbers can be calculated in any combination, but keep in mind the mathematical order of operations as you calculate:
    • First perform any calculations inside parentheses, if they exist.
    • Next perform all multiplications and divisions
    • Lastly, perform all additions and subtractions
  • In this puzzle, adjacent numbers are three numbers connected vertically, horizontally or in an “L” shape, as shown in the diagram below:

Horizontal equa
Vertical equa
L-shaped Equa

  • Use only basic arithmetic functions: addition, subtraction, multiplication, division; and follow the order of operations when necessary.

Let’s explain this in a little more detail, and you’ll get the hang of it in no time at all!

Rules of the Game

You are given a grid ranging in size from 2×3 to 6×6 and also an Equa-X number between 13 and 24. For example, let’s say you are given Equa-15. On your grid, almost all of the numbers can be connected together in threes, and using addition, subtraction, multiplication, or division, can be made to equal 15 if connected to the right numbers. (Again, “connected” means that you can connect 3 adjacent numbers together in a straight vertical, horizontal, or “L” shaped line on the grid.)

However, there is one, and only one number on the grid that CANNOT be used with ANY of the other numbers to equal 15, no matter what math you use. Your goal in each puzzle is to eliminate all other possibilities and find out which number will not work with any others! That number is your solution.

The easiest way to find the solution is to start making connections on your own. If you can connect any three numbers together in a horizontal, vertical, or “L” shaped line and cause them to equal 15 when added, subtracted, multiplied, or divided together in any order or combination, then you know those three numbers are not your answer. Instead, these numbers are clues which will help you solve the mystery!


In this 6×6 grid, our task is to find the number which can not create Equa-14, no matter what we try. In other words, when you connect that number with two numbers in a straight or “L” shaped line, the three numbers should not be able to equal 14 no matter what kind of math you do.

The only way for you to find the solution is to start matching up triplets and doing the math. After some time you’ll realize that one number on the grid stubbornly refuses to match with any other adjacent numbers to equal 14 and, in this example, that is number 6 in 2nd row, 5th column.

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