A project can be completed by team A in 60 days, team B in 30 days, and team C in 20 days. What should I do if I want to complete it within 15 days?
一项工程，甲队独做60天完成，乙队独做30天完成，丙队独做20天完成．若要在15天内完成，应该怎么办？
<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/60) + (1/20)</gadget>
<output>1/15 = around 0.066667</output>

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

<result>15</result>