Question: Find the answer to this math problem: 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=50 donated boxes
So they have a total of 50+10=60 boxes
So they need a total of 60/2=30 tables
That means they need 30-15=15 tables