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 = 
<gadget id="calculator">200*5</gadget>
<output>1_000</output>
1000 sheets of paper in a week.
Thus, there are 9000/1000 = 
<gadget id="calculator">9000/1000</gadget>
<output>9</output>
9 classes in the school.

<result>9</result>