A project can be completed by A alone in 15 days and B alone in 10 days. If A and B work together, how many days will it take to complete the project?
一项工程，甲独做15天可以完成，乙独做10天完成这．如果甲乙合做，多少天才能完成这项工程？
<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>