One job can be done by A alone in 12 days and B by himself in 15 days. Two people worked at the same time for 3 days, how much of the work was completed?
一件工作，甲独做12天完成，乙独做15天完成任务．两人同时做了3天，完成了这件工作的几分之几？
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

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

<gadget id="calculator">(1/12) + (1/15)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/20) * 3</gadget>
<output>9/20 = around 0.45</output>

<result>9/20 = around 0.45</result>