A project alone takes 30 days and B alone takes 20 days. Now the two are working together, and B didn't participate for a few days in the middle, and it took 18 days to complete the task. How many days did B not attend?
一项工程甲单独做要30天，乙单独做要20天．现在两个合做，中途乙有几天没参加，结果用了18天才完成任务．乙有几天没有参加？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) * 18</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">(2/5) / (1/20)</gadget>
<output>8</output>

<gadget id="calculator">18 - 8</gadget>
<output>10</output>

<result>10</result>