There is a bag of rice, I ate (1/5) of it for the first time, and the rest (1/2) for the second time, how much is the rest of the bag of rice.
有一袋大米，第一次吃了它的(1/5)，第二次吃了余下的(1/2)，剩下的占这袋大米的多少．
<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 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(4/5) * (1/2)</gadget>
<output>2/5 = around 0.4</output>

<result>2/5 = around 0.4</result>