A ream of paper is 4000 sheets, used up (4/5), how many sheets are left?
一令纸4000张，用去(4/5)，还剩多少张？
<gadget id="calculator">4 / 5</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">4_000 * (1/5)</gadget>
<output>800</output>

<result>800</result>