There are 52 students in the class, including 3 1 who can play the piano, 20/who can play martial arts, and 14 who can neither. How many people can have both?

52 minus 14 equals 38. 3 1 can play the piano, and 20% can learn martial arts. A total of 38 MINUS 3 1 is equivalent to killing seven people who can't play the piano. These seven people all know martial arts and can't play the piano, so you just subtract 7 from the total number of martial arts from 20, and the remaining martial arts are 13. That's probably the logic,