In a math class, the students spent (1/5) hours doing exercises, the teacher explained (3/10) hours, and the rest of the time was discussion. Each class is 40 minutes. How long did the students spend on discussion?
一堂数学课，学生做练习用了(1/5)小时，老师讲解了(3/10)小时，其余时间是讨论，每堂课40分钟，学生讨论用了多长时间？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

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

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

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

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