A piece of steel, if (1/4) is used up, there will be 9 meters left, if 40% is used up, how many meters will be left.
一根钢材，如果用去(1/4)，就剩下9米，如果用去40%，还剩多少米．
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">9 / (3/4)</gadget>
<output>12</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">12 * (3/5)</gadget>
<output>36/5 = around 7.2</output>

<result>36/5 = around 7.2</result>