Process a batch of parts and do it alone. The master completes it in 5 days (1/3), and the apprentice completes it in 4 days (1/5). The two work together to complete this batch of parts in one day ((())/(())), How many days to complete this batch of parts (7/10).
加工一批零件，单独做，师傅5天完成(1/3)，徒弟4天完成(1/5)，两人合作，一天完成这批零件的((())/(()))，多少天完成这批零件的(7/10)．
<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/3) / 5</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 4</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">(7/10) / (7/60)</gadget>
<output>6</output>

<result>6</result>