After an empty oil barrel is filled with 40% oil, the total weight of the barrel is 8.5 dry grams. When the oil barrel is filled with oil, the total weight of the barrel is 16 dry grams. At this time, 80% of the oil should be left in the oil barrel , how many kilograms of oil need to be poured from the barrel.
一个空油桶装进40%的油以后，连桶共重8.5干克，当这个油桶装满油以后，连桶共重16干克，这时要使油桶中剩下80%的油，需要从桶中倒出多少千克油．
<gadget id="calculator">16 - 8.5</gadget>
<output>7.5</output>

<gadget id="calculator">40 / 100</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">7.5 / (3/5)</gadget>
<output>12.5</output>

<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">12.5 * (1/5)</gadget>
<output>2.5</output>

<result>2.5</result>