JORIANDRAKE'S PROFILE

Okay, I plan to write a full report/review once I finish.

A girl is twice as old as her brother and half as old as her father. In 50 years, her brother will be half as old as his father. How old is the daughter now?

Managed to solve the rest of the riddles, this is the last one I have not yet in the illusion place, and I just do them all because I want to, as the road is already open.

Still, something makes no sense here, perhaps it is because English is not my native language, but I tried 50 as the answer, then 75 and even 25 out of frustration. Shouldn't the correct answer be 50? I even looked the riddle up in English and it seems to agree that the answer is 50, but despite that when I type 50 I get attacked by a monster (not the shadow death skull).

I can easy enough defeat the monster, and testing it once it seems actually just fighting through all monster encounters here would benefit me more as it grants substantial XP and loot while correctly answering seems to not give anything, but I still prefer to solve all riddles without a battle, which made me register and ask here what the answer should be, or if this riddle's question is bugged?

edit: and there is a typo in one of the book descriptions inside the library/museum