Processing a batch of parts, just complete (2/7) of the total number in three days, how much of the total number is completed on average every day.
加工一批零件，三天正好完成总数的(2/7)，平均每天完成总数的多少．
<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">(2/7) / 3</gadget>
<output>2/21 = around 0.095238</output>

<result>2/21 = around 0.095238</result>