A barrel of oil has been used up (3/5), and there are 280 kilograms left. How many kilograms of this barrel of oil are there?
一桶油，用掉了(3/5)，还剩280千克，这桶油原来有多少千克？
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">280 / (2/5)</gadget>
<output>700</output>

<result>700</result>