60% of a book has been read, and there are 80 pages left unread, how many pages have been read?
一本书读了60%，还剩下80页没有读，已读了多少页．
<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">80 / (2/5)</gadget>
<output>200</output>

<gadget id="calculator">200 * (3/5)</gadget>
<output>120</output>

<result>120</result>