conversations.from: human
conversations.value: If one fourth of the engines are defective, and there are 5 batches of 80 engines each. How many engines are not defective?
  Find the solution.
conversations.from: assistant
conversations.value: There are 80*5 = 400 engines in total.
  400/4 = 100 of the engines are defective.
  400-100 = 300 of the engines are not defective.