A rope is (5/7) meters long, and (2/5) has been used up, how many meters have been used up.
一根绳子长(5/7)米，用去了(2/5)，用去了多少米．
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(5/7) * (2/5)</gadget>
<output>2/7 = around 0.285714</output>

<result>2/7 = around 0.285714</result>