conversations.from: human
conversations.value: Tom needs to buy a new gaming system.  He trades in his super Nintendo for an original NES.  The SNES is worth $150 and the store gives him 80% of that value.  He gives $80 and gets back $10 change and a game worth $30.  How much was the NES on sale for?
  Solve it.
conversations.from: assistant
conversations.value: He traded in the SNES for 150*.8=$120
  Including the money he gave, he spent 120+80=$200
  He got 10+30=$40 in change
  So the NES cost 200-40=$160