It takes 10 days for A to complete the processing of a batch of parts, and 15 days for B to complete it alone. A and B work together, how many days will it take to process this batch of parts?
加工一批零件，甲单独完成需10天，乙单独完成需15天．甲、乙合做，加工完这批零件需多少天？
<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">1 / (1/6)</gadget>
<output>6</output>

<result>6</result>