Two engineering teams participated in the expansion of a 1,200-meter section of Jiefang Road due to municipal construction needs. Team A took 20 days to complete it alone, and Team B took 15 days to complete it alone. How much?
两个工程队因市政建设需要参与扩建一段1200米的解放路，甲队单独做要20天完成，乙队单独做要15天完成，它们各做了4天，共做了这项工程的几分之几？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/20) + (1/15)</gadget>
<output>7/60 = around 0.116667</output>

<gadget id="calculator">(7/60) * 4</gadget>
<output>7/15 = around 0.466667</output>

<result>7/15 = around 0.466667</result>