It takes 10 days for A to complete a job alone, and B's work efficiency is twice that of A. Two people cooperate, how many days can finish this work?
一件工作，甲单独完成需要10天，乙的工作效率是甲的2倍．两人合作，几天能完成这件工作？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 2</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/10) + (1/5)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / (3/10)</gadget>
<output>10/3 = around 3.333333</output>

<result>10/3 = around 3.333333</result>