A barrel of oil, if (2/5) is used, there are 9 kilograms left, if (2/3) is used, how many kilograms are left.
一桶油，如果用去(2/5)，还剩9千克，如果用去(2/3)，还剩多少千克．
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">9 / (3/5)</gadget>
<output>15</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">15 * (1/3)</gadget>
<output>5</output>

<result>5</result>