A project is done alone, team A can complete 1/4 of the project in 5 days, and team B can complete it in 15 days. How many days will it take for (2/3) of the project to be done jointly by teams A and B?
一项工程，单独做，甲队5天可完成工程的(1/4)，乙队15天全部完成．现在由甲乙两队合做工程的(2/3)，需要多少天？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) / 5</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">(2/3) / (7/60)</gadget>
<output>40/7 = around 5.714286</output>

<result>40/7 = around 5.714286</result>