There are definitely have multiply subjective answers
I think you're misunderstanding this a bit. The problem is not whether there can be multiple answers or ways to solve a puzzle, which actually happens quite often. (Otherwise, there would only be one answer per question.)
The problem is whether an answer can be determined or proven to be correct. For example, this is on-topic:
Q: How do I add 12+39?
- A1: You add 10+30=40, and then 2+9=11, and then put them together and get 51.
- A2: You add 12+40=52, and then you subtract 1 and get 51.
- A3: You add 12+30=42, and then you add 9 more and get 51.
and so on. I cannot stress this enough:
The problem is answer validity, not quantity.
Therefore, yes, these can be on-topic for the site.