Each class uses 200 sheets of paper per day. The school uses a total of 9000 sheets of paper every week. If there are 5 days of school days, how many classes are there in the school?
Each class uses 200 x 5 = <<200*5=1000>>1000 sheets of paper in a week.
Thus, there are 9000/1000 = <<9000/1000=9>>9 classes in the school.
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