A bag of noodles is eaten first (1/5) and then (1/4), how much is left.
一袋面先吃了(1/5)又吃了(1/4)，还剩多少．
<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">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">(4/5) * (3/4)</gadget>
<output>3/5 = around 0.6</output>

<result>3/5 = around 0.6</result>