This topic belongs to the application problem in mathematics. The key to solving the problem is to calculate the score (doing a right question+doing a wrong question), then divide the total loss by the score (doing a right question+doing a wrong question), and finally you can know how many questions he has done wrong.

The specific steps are as follows:

1. According to the topic, the math contest paper has *** 12 questions. If you get 9 points correctly, the total score of the math contest paper is 9 × 12 = 108 points.

2. It is known that if you do the right 1 question, you will get 9 points; if you do the wrong question, you will get 3 points. Then, Kobayashi's score (every right question+every wrong question) =9+3= his total score = 12.

3. Because Kobayashi got 84 points, the score he lost (the score he didn't get) = 108-84=24 points.

Because Xiao Lin dropped 24 points in this test paper, he was wrong =24/(9+3)=2.

Regarding the application:

Application problem is to describe relevant facts in language or words and reflect some mathematical relationship (such as quantitative relationship, etc.). ) and solved an unknown number of problems. Each application problem includes known conditions and problems.

Mathematics application problems in primary schools are usually divided into two categories: simple application problems that can be solved in one step only by addition, subtraction, multiplication and division; Complex application problems that need two or more operations to solve.