conversations.from: human
conversations.value: The number of short students in a class is 2/5 of the total number of students. If there are 90 tall students, and the class has 400 students, calculate the total number of students with average height.
  Work out the solution step by step.
conversations.from: assistant
conversations.value: The number of short students in the class is 2/5*400 = 160
  The total number of short and tall students is 160+90 = 250
  Since there are 400 students in the class, the number of students with average height is 400-250 = 150