A project is completed in 30 days by A alone, and A is completed in 20 days alone. First, A and B work together, but because B is sick, they rest for a few days. During B’s rest, A works alone. The project is completed in 15 days , How many days did B rest?
一项工程甲独做30天完成，甲独做20天完成，先由甲乙两人合作，但因乙生病，中间休息了几天，乙休息时有甲单独做，这项工程一共15天完成，乙休息了几天？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/30) * 15</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">(1/2) / (1/20)</gadget>
<output>10</output>

<gadget id="calculator">15 - 10</gadget>
<output>5</output>

<result>5</result>