conversations.from: human
conversations.value: A mother goes shopping. She buys cocoa at $4.20, laundry at $9.45 and a package of pasta at $1.35. She pays $20. How much change does the cashier give back?
  Give me a solution to this problem
conversations.from: assistant
conversations.value: The total shopping cost is $4.2 + $9.45 + $1.35 = $15.
  The cashier gives back $20 - 1$5 = $5.