project can be completed in 10 days alone, and B can be completed in 15 days alone. How many days will it take for A and B to complete the project together? (Solving problems with equations)
一项工程，甲单独做10天完成，乙单独做15天完成，甲乙一起完成这项工程需要多少天？(用方程解决问题)
<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>