A barrel of oil has been used up (1/5), and there are 280 kilograms left. How many kilograms of this barrel of oil are there?
一桶油，用掉了(1/5)，还剩280千克，这桶油原来有多少千克？
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">280 / (4/5)</gadget>
<output>350</output>

<result>350</result>