bottle of oil weighs 500 grams, eat 40% and add the remaining 40%, what is the weight of this bottle of oil in grams
一瓶油重500克，吃掉40%，再增加剩下的40%，这时这瓶油重多少克
<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">1 + (2/5)</gadget>
<output>7/5 = around 1.4</output>

<gadget id="calculator">500 * (3/5) * (7/5)</gadget>
<output>420</output>

<result>420</result>