A project takes 10 days for A to complete alone, and 15 days for B to complete alone. After the two teams worked together for 3 days, how much of the project was completed.
一项工程，甲独修要10完成，乙独修要15天完成．两队合修3天后，完成了这项工程的多少．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) + (1/15)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">3 * (1/6)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>