A class lasts 40 minutes, the teacher spends (1/3) hour lecturing, students spend (1/6) hour communicating and discussing, and the rest of the time students do homework, how much time do students spend on homework?
一节课40分钟，老师讲课用去(1/3)小时，学生交流讨论用去(1/6)小时，余下的时间学生写作业，学生写作业用去多少时间？
<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 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(2/3) - (1/3) - (1/6)</gadget>
<output>1/6 = around 0.166667</output>

<result>1/6 = around 0.166667</result>