There are 10 dormitories in a certain school, and 80 students are just full. There are three types of dormitories, 10 students live in a big room, 7 students live in a middle room, 5 students live in a small room, and the middle room is the most. How many rooms are there.
某校有10间宿舍，80个学生刚好住满．宿舍有三种规格，大房间住10个学生，中房间住7个学生，小房间住5个学生，其中中房间最多．中房间有多少间．
<result>5</result>