A wire is 20 meters long, (2/5) of it is used up for the first time, and 9 meters are used up for the second time, how many meters are left?
一根电线长20米，第一次用去它的(2/5)，第二次又用去9米，还剩多少米．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">20 * (2/5)</gadget>
<output>8</output>

<gadget id="calculator">20 - 8 - 9</gadget>
<output>3</output>

<result>3</result>