After 70% of a whole barrel of gasoline is used up, another 10 kilograms of gasoline is poured into the barrel. At this time, the gasoline in the barrel is exactly half of the original full barrel of gasoline. How many kilograms does the original full barrel of gasoline weigh?
一整桶汽油，在用去70%以后，又向桶内倒入10千克汽油．这时，桶内汽油正好是原来整桶汽油的一半，原来这一整桶汽油重多少千克．
<gadget id="calculator">50 / 100</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">(1/2) - (3/10)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 / (1/5)</gadget>
<output>50</output>

<result>50</result>