If there are less than 55 students in a class, in a test, (1/7) students get excellent, (1/3) students get good, and (1/2) students pass, how many students fail in total?
某班人数不到55人，一次测验中有(1/7)的学生得优，(1/3)的学生得良，(1/2)的学生及格，则共有多少个学生不及格．
<gadget id="calculator">2 * 3 * 7</gadget>
<output>42</output>

<gadget id="calculator">1 / 7</gadget>
<output>1/7 = around 0.142857</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 - (1/7) - (1/3) - (1/2)</gadget>
<output>1/42 = around 0.02381</output>

<gadget id="calculator">42 * (1/42)</gadget>
<output>1</output>

<result>1</result>