question: An electronics seller bought 5 phones for $700 each and gives the seller $4000 in dollar bills. How much will the seller give back in change?
answer: The seller bought the 5 phones for $700 * 5 = $<<700*5=3500>>3500.
  So the seller gives back $4000-$3500 = $<<4000-3500=500>>500.
  #### 500