barrel of gasoline, 30% of the total is used for the first time, and 20% of the total is used for the second time, leaving 50 kg. How many kilograms does this barrel of gasoline weigh?
一桶汽油，第一次用去总数的30%，第二次用去总数的20%，还剩50千克．原来这桶汽油有多少千克？
<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">50 / (1/2)</gadget>
<output>100</output>

<result>100</result>