A project, A alone in 12 days to complete the project (4/5), B alone in 15 days to complete half of the project. How many days can A and B cooperate to complete the whole project?
一项工程，甲单独做12天完成工程的(4/5)，乙单独做15天完成工程的一半．甲、乙合作，多少天可以完成全部工程？
<gadget id="calculator">4 / 5</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(4/5) / 12</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / 15</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/15) + (1/30)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / (1/10)</gadget>
<output>10</output>

<result>10</result>