In an exam, among the students who participated (1/7) got excellent, (1/3) got good, (1/2) got middle, and the rest got poor. It is known that there are less than 50 students who took the test, so the score is poor How many students are there.
一次考试，参加的学生中有(1/7)得优，(1/3)得良，(1/2)得中，其余的得差，已知参加考试的学生不满50人，那么得差的学生有多少人．
<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>