It takes 9 days for A to complete a job alone, and B’s work efficiency is twice that of A. When two people work together at the same time, how many days can they complete this job?
一件工作，甲单独完成要9天，乙的工效是甲的2倍两人同时合做，几天能完成这件工作？
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/9) * 2</gadget>
<output>2/9 = around 0.222222</output>

<gadget id="calculator">(1/9) + (2/9)</gadget>
<output>1/3 = around 0.333333</output>

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

<result>3</result>