The original plan arranges several people to carry out a certain task. If 10 people are added, it can be completed in 6 days; if 15 people are added, it can be completed in 5 days. So how many days can the original plan be completed? (everyone works at the same efficiency)
原计划安排若干人进行某项任务，如果增加10人，6天可以完成；如果增加15人，5天可以完成．那么原计划多少天可以完成．(每人工作效率相同)
<gadget id="calculator">5 * 15</gadget>
<output>75</output>

<gadget id="calculator">6 * 10</gadget>
<output>60</output>

<gadget id="calculator">75 - 60</gadget>
<output>15</output>

<gadget id="calculator">6 - 5</gadget>
<output>1</output>

<gadget id="calculator">15 / 1</gadget>
<output>15</output>

<gadget id="calculator">15 + 10</gadget>
<output>25</output>

<gadget id="calculator">25 / 15 / 1</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">6 * (5/3)</gadget>
<output>10</output>

<result>10</result>