1. In a class there are 52 students. Each student in the class participates in at least one of 3 extracurricular sports, namely football, badminton and basketball. The following facts are known: - students who follow badminton also follow football, - there are 39 students who follow football, - there are 22 students who follow basketball, - 18 people only follow football - 4 people take all three extracurriculars How many students participate in badminton? Also determine the number of students who follow badminton only

2.In one class, the ratio of the number of students taking part in learning to use Java, C, and Pascal software is 5:4:3 . It is known that: There are 50 students studying Java; 10% of them also learn C and Pascal at the same time; 20% of them learn C and 20% learn Pascal. 10 students who studied Pascal and C but did not learn Java. Draw a venn diagram, How many students only study Pascal?

3. Use the properties of set operations to prove that : for each set A and, B

holds ( ) = B