question: John is raising money for a school trip. He has applied for help from the school, which has decided to cover half the cost of the trip. How much money is John missing if he has $50 and the trip costs $300?
answer: John's school has decided to pay 300 / 2 = $<<300/2=150>>150 for his trip.
  In total John has covered 150 + 50 = $<<150+50=200>>200 for his trip
  Therefore, John needs 300 - 200 = $<<300-200=100>>100 more for the trip.
  #### 100