conversations.from: human
conversations.value: Roxanne bought 2 cups of lemonade for $2 each and 2 sandwiches for $2.50 each. How much change must she get from a $20 bill?
conversations.from: assistant
conversations.value: Two cups of lemonade amount to $2 x 2 = $4.
  Two sandwiches amount to $2.50 x 2 = $5.
  So, the total amount that Roxanne had to pay was $4 + $5 = $9.
  Thus, her change must be $20 - $9 = $11.