barrel of oil is used up (2/5) on the first day, and 10 kg is used up on the second day, and half is left at this time. How many kilograms is this barrel of oil originally?
一桶油第一天用去(2/5)，第二天用去10千克，这时还剩一半．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">2 / 5</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>