A barrel of gasoline, 30% of the total amount is used for the first time, and (1/5) of the total amount is used for the second time, leaving 50L. How many liters is there in this barrel of gasoline?
一桶汽油，第一次用去总数的30%，第二次用去总数的(1/5)，还剩50L，这桶汽油原来有多少升？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 5</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>