conversations.from: human
conversations.value: To buy a book, you pay $20 for each of the first 5 books at the supermarket, and for each additional book you buy over $20, you receive a discount of $2. If Beatrice bought 20 books, how much did she pay at the supermarket?
conversations.from: assistant
conversations.value: For the first five books, the total cost is $20*5 = $100
  For every additional book over $5, you pay $2 less, totaling to $20-$2 = $18
  Beatrice bought 20 books, so the number of books at which she received the $2 discount is 20-5 = 15 books.
  For the 15 books, Beatrice paid 15*$18 = $270
  In total, Beatrice paid $100+$270 = $370 for the 20 books.