The key to doing this problem is to find out how many problems only one person can solve. How many problems have two people solved? How many did three people solve? According to the problems, it is certain that 50 problems have been solved. Obviously, if three people are exactly the same, it can only be 30. If the three are completely different, it is 90. The problem now is 50 questions, and three people have solved 30 questions each. Because the problem is only the difference between a difficult problem and an easy problem, it can be determined that no two people can solve the same problem at the same time, so it can be determined that 20 problems are solved by three people at the same time, and 10 problems are solved by three people respectively. Only in this way can it be a description of the topic. So there are still many questions and easy questions.