Japanese puzzle website Notore Biyori has published a matchstick brain teaser featuring the flawed equation 9 + 83 = 80 that requires moving one stick.
Under the rules of the puzzle, players must fix the calculation by shifting a single matchstick without adding new sticks or throwing any away. Every digit and mathematical symbol must retain a clear, valid shape once the move is complete.
The original formula presents an obvious contradiction. Adding two positive numbers cannot produce an answer smaller than either of them, yet eighty is smaller than eighty-three before nine is even added. In regular arithmetic, nine plus eighty-three equals ninety-two.
Because the numbers are built out of individual matchsticks, the error cannot be solved by standard pencil-and-paper methods. Success depends on recognizing how the lines of each numeral can change when one element is relocated.
How to solve the equation
To reach the correct answer, the player must alter both the first number in the sum and the total after the equals sign. The middle number, eighty-three, and the plus sign remain completely untouched throughout the move.
The first step focuses on the digit nine at the start of the formula. Removing the vertical matchstick from the upper right section of the nine transforms the figure into a five.
The solver then carries that loose matchstick across to the number eighty. Placing the stick horizontally through the center of the zero turns it into an eight, converting eighty into eighty-eight.
The revised equation reads 5 + 83 = 88. Five plus eighty-three equals eighty-eight, making the calculation correct while keeping every symbol properly formed.
Recreational mathematics and brain training
Matchstick arithmetic problems belong to a long tradition of recreational mathematics. The puzzles rely on the geometry of seven-segment displays, the standardized layout used on digital wristwatches, alarm clocks, and electronic calculators.
In a seven-segment system, digits share identical line positions. A zero lacks only the central bar to become an eight, while a nine can turn into a five or a three with the adjustment of a single stroke. Solvers must balance mathematical calculations with spatial reasoning to spot compatible pairs.
The creator of the puzzle, Notore Biyori, specializes in daily logic exercises. The Japanese term notore is a widespread abbreviation for brain training, referring to mental agility games that encourage active deduction and pattern recognition.
Related arithmetic challenges
Ukrainian news outlet UNIAN, which circulated the matchstick puzzle with an illustrated diagram, pointed readers toward several other arithmetic tests. These include a sequence riddle where solvers must identify the next number in a pattern.
Other challenges test knowledge of the order of operations. One problem asks readers to solve 9 - 3 : 1/3 + 1, which features an unusual division step, while another presents 9 + 12 : 3 x 2 with three arithmetic operations. A third puzzle asks which three mathematical signs can turn four twos into six in the formula 2 2 2 2 = 6.
