A set of furniture is completed by an old worker in 40 days and by an apprentice in 80 days. Now it is done by an old worker and an apprentice, how many days can it be completed?
一套家具，由一个老工人做40天完成，由一个学徒工做80天完成．现由一个老工人和一个学徒工一起做，几天可以完成？
<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / 80</gadget>
<output>1/80 = around 0.0125</output>

<gadget id="calculator">(1/40) + (1/80)</gadget>
<output>3/80 = around 0.0375</output>

<gadget id="calculator">1 / (3/80)</gadget>
<output>80/3 = around 26.666667</output>

<result>80/3 = around 26.666667</result>