Solution: List the possibility that the sum of each number and the other two numbers is 45: Yizhi 15 has four different combinations, other odd numbers are two different combinations, and even numbers are three different combinations.

In nine grids, the center needs the same number of four different combinations, so fill in 15.

Vertex needs the same number of three different combinations, so fill in four even numbers.

The top, bottom, left and right cells need the same number of two different combinations, so fill in four odd numbers.

Find a routine method:

1, serial number: to find a regular topic, a series of quantities arranged in a certain order are usually given, and we are required to find a general rule according to these known quantities. Find out the rule, usually the serial number of the package. Therefore, it is easier to find the mystery by comparing variables with serial numbers.

2. Fibonacci sequence method: each number is the sum of the first two numbers.

3. Arithmetic series method: the difference between every two numbers is equal.

4. Tabbing method: You can look at it every once in a while to see what the relationship between the separated numbers is, for example, 14, 1, 12, 3, 10, 5, odd items become arithmetic progression, even items also become arithmetic progression, and then you have to fill in 8.