Precisely

100 200 300

400 500 600

700 800 900

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.