Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given n rectangles represented by a 0-indexed 2D integer array rectangles, where rectangles[i] = [widthi, heighti] denotes the width and height of the ith rectangle.
Two rectangles i and j (i < j) are considered interchangeable if they have the same width-to-height ratio. More formally, two rectangles are interchangeable if widthi/heighti == widthj/heightj (using decimal division, not integer division).
Return the number of pairs of interchangeable rectangles in rectangles.
 
Please complete the following python code precisely:
```python
class Solution:
    def interchangeableRectangles(self, rectangles: List[List[int]]) -> int:
```