conversations.from: human
conversations.value: There are 40 students in the 6th  grade.  25% of them wear glasses and 40% of them wear contact lenses.  How many students do not wear any vision assistance wear?
  Can you solve this problem?
conversations.from: assistant
conversations.value: There are 40 x 25% = 10 students who wear glasses.
  There are 40 x 40% = 16 students who wear contact lenses.
  There are 10 + 16 = 26 students who wear vision assistance.
  There are 40 - 26 = 14 students who do not wear any vision assistance wear.