According to the air quality monitoring statistics of a city in November 2014, the number of days with "excellent" air quality accounted for (2/5) of the total number of days, the number of days with "good" air quality accounted for (1/3) of the total number of days, and the rest were seriously polluted. What percentage of the total number of days are heavily polluted days?
某市2014年11月份空气质量监测统计显示，空气质量"优"的天数占总天数的(2/5)，"良"的天数占总天数的(1/3)，其余均受到严重污染，受到严重污染的天数占总天数的几分之几？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 - (2/5) - (1/3)</gadget>
<output>4/15 = around 0.266667</output>

<result>4/15 = around 0.266667</result>