Maximum Average Pass Ratio

There is a school that has classes of students and each class will be having a final exam. You are given a 2D integer array `classes`, where `classes[i] = [passi, totali]`. You know beforehand that in the `ith` class, there are `totali` total students, but only `passi` number of students will pass the exam. You are also given an integer `extraStudents`. There are another `extraStudents` brilliant students that are **guaranteed** to pass the exam of any class they are assigned to. You want to assign each of the `extraStudents` students to a class in a way that **maximizes** the **average** pass ratio across **all** the classes. The **pass ratio** of a class is equal to the number of students of the class that will pass the exam divided by the total number of students of the class. The **average pass ratio** is the sum of pass ratios of all the classes divided by the number of the classes. Return _the **maximum** possible average pass ratio after assigning the _`extraStudents`_ students. _Answers within `10-5` of the actual answer will be accepted.   **Example 1:** **Input:** classes = [[1,2],[3,5],[2,2]], `extraStudents` = 2 **Output:** 0.78333 **Explanation:** You can assign the two extra students to the first class. The average pass ratio will be equal to (3/4 + 3/5 + 2/2) / 3 = 0.78333. ``` **Example 2:** **Input:** classes = [[2,4],[3,9],[4,5],[2,10]], `extraStudents` = 4 **Output:** 0.53485 ```   **Constraints:** - `1 <= classes.length <= 105` - `classes[i].length == 2` - `1 <= passi <= totali <= 105` - `1 <= extraStudents <= 105`