A class is 40 minutes. The teacher explains (1/4) hour, and the students cooperate and explore (1/3) hour. The rest do exercises, how many hours do exercises?
一节课40分钟．老师讲解用(1/4)小时，学生合作探究用(1/3)小时．其余做练习，做练习多少小时？
<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">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/4) + (1/3)</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">(2/3) - (7/12)</gadget>
<output>1/12 = around 0.083333</output>

<result>1/12 = around 0.083333</result>