Students whose number is a multiple of 3 take part in the rope skipping competition: 30/3= 10, so there should be 10, but the people who take part in table tennis and those who jump rope cross (for example, they can take part in rope skipping on the 6th, but they should take part in table tennis, so they should be removed. ) Calculate its least common multiple of 2*3=6, 30/6=5, then 10 people who should take part in the skipping competition should subtract 5 people who have already taken part in the table tennis competition, 10-5=5. The last five people went to jump rope competition.
Students whose number is multiple of 5 take part in gymnastics competition: 30/5=6. There should be six people, but as mentioned above, there may be overlap.
2 * 5 2*5= 10/0,30/10 = 3, so there are three people who overlap with table tennis.
3 * 5 =15,30/15 = 2, so there are two people overlapping in skipping rope.
2*3*5=30, 30/30= 1, gymnastics, rope skipping, table tennis and 1 person overlap and are included in 2 and 3.
6-((3+2)- 1)=2, so two people take part in gymnastics.
It is easiest for you to draw a circle.