40% of a barrel of oil is used on the first day, 10 kilograms are used on the second day, and half of the barrel of oil is used in two days. How much is the original price of this barrel of oil in kilograms?
一桶油第一天用去它的40%，第二天用去10千克，两天正好用去这桶油的一半，这桶油原价多少千克？
<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">(1/2) - (2/5)</gadget>
<output>1/10 = around 0.1</output>

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

<result>100</result>