According to the rule of going to the two ends of the serial number, three numbers are typed in the five-element connection, 4, 6 and 8.

This skill comes from the ancient mathematical problems in China, also called "Twelve Rings Diagram", which is a common problem-solving idea, aiming at finding the solution through the association of numbers. Including five different connection methods, such as: go to two ends to see five connections, go to one end to see five connections, go to two ends to see three connections, go to one end to see three connections, extension line method. This skill can be used not only in mathematical problems, but also in solving problems in Chinese, English, physics and other disciplines.