Answer: 4 is to 2
Explanation:
This is almost like a mind tricking question.
The question asked number of tetras to catfishes.
so you only have to focus on that. Not other unnecessary details
They gave you, 4 tetras, 9 corydoras, and 2 synodontis catfishes.
So the ration would be 4 tetras to 2 catfishes.