40% of a barrel of oil is used on the first day, and 10 kg is used on the second day, leaving (1/2). How many kilograms is this barrel of oil originally?
一桶油第一天用去40%，第二天用去10千克，还剩下(1/2)．这桶油原来有多少千克？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">10 / (1/10)</gadget>
<output>100</output>

<result>100</result>