A project alone will take 15 hours and B alone will take 10 hours. How many hours can A and B cooperate to complete the project now?
一项工程，甲单独完成要15小时，乙单独完成要10小时．现在由甲、乙合作多少小时可以完成这项工程．
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">1 / (1/6)</gadget>
<output>6</output>

<result>6</result>