conversations.from: human
conversations.value: Find the answer to the math problem: There are 20 students in Miss Susan's class. 5 of them are good at math only, 8 of them perform well in English only, and the rest are good at both math and English. How many are good at math?
conversations.from: assistant
conversations.value: The number of students who are good at math includes those who are only good at math and those who are good at both math and English. The only group that isn't included is the students who are only good at English.
  There are 20 - 8 = 12 students who are good at math.