conversations.from: human
conversations.value: An alien invades Earth.  It abducts 200 people.  He returns 80% of the people abducted.  After that he takes 10 people to another planet.  He took the rest to his home planet.  How many people did he take to his home planet?
  Give me a solution to this problem
conversations.from: assistant
conversations.value: He returned 200*.8=160 people
  So he had 200-160=40 people
  He took 10 of those to another planet so he took 40-10=30 to his home planet