There are five major questions in this test paper. When the elf was doing this test paper, he spent (1/3) hours on the first and second major questions, and spent (1/2) hours on the third and second major questions. Four major questions, and finally finished the fifth question in (1/4) hour. How much time does the elf have left to check? (Note: 80 minutes to complete the volume)
本试卷共有五大题，小精灵做这张试卷时，用(1/3)小时做好了第一大题和第二大题，用(1/2)小时做好了第三大题和第四大题，最后用(1/4)小时完成了第五大题．小精灵还有多少时间用来检查？(注意：完卷时间80分钟)
<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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

<gadget id="calculator">(1/3) + (1/2) + (1/4)</gadget>
<output>13/12 = around 1.083333</output>

<gadget id="calculator">(4/3) - (13/12)</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>