A certain class counted math scores, the average score was 85.13, and after the review, it was found that Li Xiaona's score of 87 was mistaken for 78 points. After recalculation, the average score of the class was 85.31. How many students are there in this class?
某班统计数学成绩，平均成绩为85.13，事后复查，发现将李小娜的成绩87分误成78分，经重新计算后该班平均成绩是85.31，这个班有多少个同学？
<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>