That's true, change of long was only 10 degrees, the maximum the convergency could possibly be was ch long, 10 degrees, and that only at the pole. Max possible conversion angle is therefore 5 degrees, so only one possible answer. Having said that a solution with that sort of detached view would be quite a thing to expect from a student at the very start of their studies, it would be much more likely they would whip through the convergency formula to find a more accurate answer, but with less mental effort.