In a class of 40 minutes, the teacher spent (3/10) hours on the explanation, (1/5) hours on the experiment, and the rest of the time the students did their homework, how many hours did the students spend on their homework?
一节课40分钟，老师讲解用了(3/10)小时，做实验用了(1/5)小时，剩下的时间学生做作业，学生做作业用了多少小时？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(2/3) - (3/10) - (1/5)</gadget>
<output>1/6 = around 0.166667</output>

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