For a barrel of pesticides, pour out (2/7) for the first time and then pour 120 grams back into the barrel, pour out the remaining pesticide (3/8) in the barrel for the second time, pour out 320 grams for the third time, and pour out 320 grams in the barrel for the third time. The remaining 80 grams, how many grams of pesticides are in the barrel.
一桶农药，第一次倒出(2/7)然后倒回桶内120克，第二次倒出桶中剩下农药的(3/8)，第三次倒出320克，桶中还剩下80克，原来桶中有农药多少克．
<gadget id="calculator">320 + 80</gadget>
<output>400</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">1 - (3/8)</gadget>
<output>5/8 = around 0.625</output>

<gadget id="calculator">400 / (5/8)</gadget>
<output>640</output>

<gadget id="calculator">640 - 120</gadget>
<output>520</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">520 / (5/7)</gadget>
<output>728</output>

<result>728</result>