football ticket is 30 yuan, and after the price reduction, the audience doubles and the income increases (1/5). How much does a ticket drop in price?
足球门票30元一张，降价后观众增加一倍，收入增加(1/5)．一张门票降价多少元．
<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(6/5) / 2</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">30 * (3/5)</gadget>
<output>18</output>

<gadget id="calculator">30 - 18</gadget>
<output>12</output>

<result>12</result>