Questions & Answers about Ratkaisu oli nerokas.
- ratkaisu = a noun: solution
- oli = the past tense of olla (to be): was
- nerokas = an adjective: ingenious / brilliant / clever
So the sentence structure is:
noun + verb + adjective
That is very normal in Finnish.
Because it is the subject of the sentence, and the subject is often in the nominative (the dictionary form).
Here, ratkaisu is the thing being described:
- Ratkaisu = the solution
- oli nerokas = was ingenious
So ratkaisu stays in its basic nominative singular form.