Tickets for a football game are 20 yuan per ticket. After the price is reduced, the audience doubles and the income increases by one-fifth. Ask how much the price of a ticket will be reduced.
足球赛门票20元一张，降价后观众增加一倍，收入增加五分之一，问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">20 * (3/5)</gadget>
<output>12</output>

<gadget id="calculator">20 - 12</gadget>
<output>8</output>

<result>8</result>