For a barrel of oil, 30% of the total is used for the first time, and 20% of the total is used for the second time. There are 60 kg left. How many kilograms is this barrel of oil originally?
一桶油，第一次用去了总数的30%，第二次用去了总数的20%．还剩下了60千克．这桶油原来有多少千克？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (3/10) - (1/5)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">60 / (1/2)</gadget>
<output>120</output>

<result>120</result>