A project can be completed by team A alone in 10 days, and team B can only complete it in 4 days alone (4/15), how many days can team A and B work together to complete?
一件工程，甲队独做10天完成，乙队独做4天只能完成(4/15)，甲、乙合做，几天可以完成？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">4 / 15</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">(4/15) / 4</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>