A disc can record 600 megabytes of data, and 80% of it has been used. How many megabytes of blank space are left?
一张光盘能刻录资料600兆，现已用它的80%，还剩下多少兆空白部分？
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">600 * (1/5)</gadget>
<output>120</output>

<result>120</result>