It takes 60 hours to organize a batch of books by one person alone. Now let some people tidy up for one hour first, and then add 15 people to tidy up with them for another two hours, just to complete the tidying work. Assuming that everyone has the same work efficiency, how many people are arranged first.
整理一批图书，如果由一个人单独做需要60小时．现由一部分人先整理一小时，随后增加15人和他们一起又整理两小时，恰好完成整理工作．假设每个人的工作效率相同，那么先安排整理的人有多少个．
<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">(1/60) * 2 * 15</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/60) * 2</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/60) + (1/30)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/2) / (1/20)</gadget>
<output>10</output>

<result>10</result>