The right answer here is not a single correct number, but a handful of correct technique or methodology. Counting the number of rainy days in the last x days would be one possible method of prediction. There are many wrong ones too, like "rain has four letters, so it's 4%" or "there are two choices, so it's 50%."

I hope the teacher taught the students which answers were right and which were wrong. If they did then I retract my criticism, even though that wasn't clear in the article.