A project, if A alone, A needs 10 days to complete, B needs 15 days to finish, C needs 20 days to finish. Now there are 3 people working together, A takes a break for 1 day in the middle, B takes a 3-day break, and C works until the completion of the project. How many days will it take to complete the project?
一项工程，如果甲单独做，甲需10天完成，乙需15天完成，丙需20天完成．现在3人合作，中途甲先休息1天，乙在休息3天，而丙一直工作到完工为止．这样一共需要多少天完成工程？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">3 / 15</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/10) + (1/5) + 1</gadget>
<output>13/10 = around 1.3</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

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

<gadget id="calculator">(1/10) + (1/15) + (1/20)</gadget>
<output>13/60 = around 0.216667</output>

<gadget id="calculator">(13/10) / (13/60)</gadget>
<output>6</output>

<result>6</result>