After 60% of some money is used, 280 yuan is left. If (2/7) is used up, how much should be left.
一些钱用去60%后剩下280元．如果用去(2/7)，应剩下多少元．
<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">280 / (2/5)</gadget>
<output>700</output>

<gadget id="calculator">2 / 7</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">1 - (2/7)</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">700 * (5/7)</gadget>
<output>500</output>

<result>500</result>