In a mathematics test, the scores of 5 students in descending order are 75 points, 82 points, A points, 87 points, and 91 points. What is their average score?
一次数学考试，5名同学的分数从小到大排列是75分、82分、a分、87分、91分，它们的平均分可能是多少分、
<result>84</result>