Math Trick Has People Asking “Why Weren’t We Taught This In School?”

Math Trick Has People Asking “Why Weren’t We Taught This In School?”


Math, though we promise you it really isn’t that daunting when you sit down and study it, has a reputation for being a tough subject. People can be put off by the basics, like multiplication, without even getting to the really difficult (and interesting) stuff like bunkbed conjectures and the Mandelbrot set.

But there are tricks for multiplication (and percentages) that can help you get to the answer more quickly. One of these went viral on X recently, which turns multiplication into a simple game of counting dots.

The “trick”, which is taught in Japanese schools, involves drawing parallel lines to represent the digits you are multiplying together (e.g. vertically), with the second set of digits intercepting them going the other way (e.g. along the horizontal).

The sum 32 x 4.

The first step, with the vertical lines representing 32 separated by a gap.

Image credit: © IFLScience

Once you have drawn the second set of lines, you merely have to count up the number of intersecting lines in each section to get your answer. Looking at it, you can probably work out what is going on. On the left is the smallest number; on the right, the largest. All of these in the example below are multiplied by 4, due to the four lines intersecting them, giving you the answer.

Japanese multiplication method for 32 x 4.

Count up the intersecting points to get your answer quickly.

Image credit: © IFLScience

The trick works with more difficult sums, though you have to separate the crossed lines into several sections.

Japanese math trick for calculating 24 x 32

In the top left, the largest numbers are multiplied together; in the bottom right, the smallest.

Image credit: © IFLScience

Unfortunately, like in multiplication taught elsewhere, there is no way of getting around carrying the one. For really difficult sums, there is always a trusty calculator. However, the Japanese method of multiplication can help to give younger folk a more intuitive way of doing sums, turning it mainly into drawing lines and counting dots.



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