certain project needs to be completed in 100 days. At the beginning, 10 people completed (1/5) of the whole project in 30 days, and then 10 more people were added to complete the project. How many days can the task be completed in advance?
某项工程需要100天完成，开始由10个人用30天完成了全部工程的(1/5)，随后再增加10个人来完成这项工程，那么能提前多少天完成任务．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">10 * 30</gadget>
<output>300</output>

<gadget id="calculator">(1/5) / 300</gadget>
<output>1/1_500 = around 0.000667</output>

<gadget id="calculator">10 + 10</gadget>
<output>20</output>

<gadget id="calculator">(1/1_500) * 20</gadget>
<output>1/75 = around 0.013333</output>

<gadget id="calculator">(4/5) / (1/75)</gadget>
<output>60</output>

<gadget id="calculator">100 - 30 - 60</gadget>
<output>10</output>

<result>10</result>