In a 40-minute physical education class, the students first spend (1/15) hours doing warm-up activities, then the teacher spends (1/3) hours explaining and demonstrating, and the rest of the time students are free to play, how many hours are the students free to play?
一节40分钟的体育课，学生先用(1/15)小时做准备活动，接下来教师用(1/3)小时讲解示范，其余时间学生自由活动，学生自由活动的时间是多少小时？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

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

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