wire is (5/7) meters long, if (1/5) is cut off, how many meters are left?
一根铁丝长(5/7)米，截去了(1/5)，还剩多少米．
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

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

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(5/7) * (4/5)</gadget>
<output>4/7 = around 0.571429</output>

<result>4/7 = around 0.571429</result>