Look at the line on the left first. The number of two vertices is 5 and 1 respectively, so the middle number should be 3. The numbers at the two endpoints of this line on the right are 5 and 3, and the middle number should be1; The numbers at the two endpoints of the bottom line are 1 and 3, and the middle number should be 5.
In arithmetic
Addition has several important properties. It is interchangeable, which means that the order is not important, it is interrelated, which means that when more than two numbers are added, the order in which the addition is performed is not important. Repeatedly adding 1 is the same as counting; Adding 0 will not change the result. Addition also follows related operations such as subtraction and multiplication.
Addition is one of the simplest digital tasks. The most basic addition: 1+ 1 five-month-old babies and even other animal species can be counted. In primary education, students are taught to calculate the superposition of decimal numbers, starting with one digit, and gradually solving the more difficult number calculation.