The average score of a certain class of statistical mathematics test is 85.13 points. After the review, it was found that Xiaoling's score of 87 was mistakenly calculated as 78. After recalculation, the average score of the class was 85.31. How many students are there in this class.
某班统计数学考试成绩，平均成绩为85.13分．事后复查，发现将小玲的成绩87分误作78分计算，经重新计算后，该班平均成绩是85.31分．这个班有多少个个学生．
<gadget id="calculator">87 - 78</gadget>
<output>9</output>

<gadget id="calculator">85.31 - 85.13</gadget>
<output>0.18</output>

<gadget id="calculator">9 / 0.18</gadget>
<output>50</output>

<result>50</result>