In a class of (2/3) hours, the students spent (1/4) hours in self-study, the teacher spent (3/10) hours in explaining, and the rest of the time for practice. How long did it take you to do the exercises?
一节课(2/3)小时，学生自学用了(1/4)小时，老师讲解用了(3/10)小时，其余时间做练习．做练习用了多长时间？
<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(2/3) - (1/4) - (3/10)</gadget>
<output>7/60 = around 0.116667</output>

<result>7/60 = around 0.116667</result>