question: A charity group decides to do a yard sale.  10 people donate 5 boxes of stuff each.  They also have 10 boxes of stuff already.  They can fit 2 boxes worth of stuff per table.  If they already own 15 tables, how many new tables do they need?
answer: There were 10*5=<<10*5=50>>50 donated boxes
  So they have a total of 50+10=<<50+10=60>>60 boxes
  So they need a total of 60/2=<<60/2=30>>30 tables
  That means they need 30-15=<<30-15=15>>15 tables
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