This problem is a simple mathematical problem. We need to find a number, which is five times and more than 20 times that of A. Suppose this number is X and A is a known number. According to the topic, we can establish the equation, x=5×a+20. This equation tells us that X is five times that of A+20. Now, if A is a specific number, we can use this equation to find the value of X. If a= 10, then x=70.

The skill of solving a problem in mathematics requires first reading the problem carefully and understanding the situation and problems described by the problem. Pay special attention to the key words in the topic, such as multiple, more, less, etc. According to the topic, define the required variables and establish a mathematical model. Find out the key information in the topic, such as twice as much, 50% less, etc. This will help to establish mathematical equations. According to the key information, the corresponding mathematical equation is established. If the problem is complex, it may be necessary to establish multiple equations. Solving equations is the key step to solve problems.

Some problems may be relatively simple and can be directly calculated; Some problems may need to be solved by calculator or computer software. Substitute the solution into the original question to see if it meets the requirements of the topic. If yes, the answer is correct; If not, you need to re-check the steps and answers.

Classification of multiple mathematical problems;

1, classified according to the involved mathematical knowledge points: it can be divided into integer multiple problems, fractional multiple problems, etc. Integer multiples mainly involve integer multiples, decimal multiples involve decimal multiples, and fractional multiples involve fractional multiples.

2. Classification by form: it can be divided into fill-in-the-blank questions, multiple-choice questions, judgment questions, calculation questions, etc. Fill-in-the-blank questions mainly test students' understanding of multiple relationships, multiple-choice questions and judgment questions mainly test students' mastery and application ability of multiple relationships, and calculation questions mainly test students' calculation ability and application ability.

3. Classification by topic difficulty: It can be divided into simple questions, medium difficulty questions and difficult questions. Simple problems are mainly some basic multiples, while moderately difficult problems need to be calculated and analyzed on the basis of understanding the multiple relationship, while more difficult problems may require students to use advanced mathematical methods and skills to solve them.

4. According to the practical problems involved, it can be divided into geometric multiples, algebraic multiples and probability multiples. Geometric multiples mainly involve the multiples of geometric figures such as area and volume, algebraic multiples mainly involve the multiples of variables, and probability multiples mainly involve the multiples of probability.