my country produces about 3.5 billion tons of industrial sewage every year, of which only (3/10) of the sewage has been treated. How many billion tons of untreated sewage are there each year?
我国每年约产生35亿吨的工业污水，其中只有(3/10)的污水经过处理，每年没有经过处理的污水大约有多少亿吨？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">35 * (7/10)</gadget>
<output>49/2 = around 24.5</output>

<result>49/2 = around 24.5</result>