For a batch of parts, the apprentice processes 25 pieces per hour, which takes 36 hours to complete. The master processes 30 per hour. How many hours does the master need to complete this batch of parts? (Solve with ratio)
一批零件，徒弟每小时加工25个，需要36小时完成．师傅每小时加工30个．师傅完成这批零件需要多少小时？(用比例解)
<gadget id="calculator">25 * 36</gadget>
<output>900</output>

<gadget id="calculator">900 / 30</gadget>
<output>30</output>

<result>30</result>