Would במיץ be a correct way to say "in the juice"? It seems weird to me to use בתוך since that means inside, right?
The word במיץ just means "in the juice"; to say בתוך המיץ means INSIDE the juice. It's just a more specific translation of the sentence Duo gave us (as little sense as it does make....).
It marked "within" wrong but I'm assuming that should be marked correct as its one of the definitions given and makes sense within the sentence (as much as fish swimming in juice makes sense at all!)
I think it's a definition issue. They like literal translations..which will be helpful to us down the line when you can differentiate between inside /within.בְּתוֹך an actual object or inside / within bifnim בפנים . (I'm just learning too, but I noticed the translating we would use colloquially isn't as helpful when learning vocab).
You remember vocabulary better with weird sentences . It's part of the science of memory and language. www.fluent-forever.com has great information on this & how to use the science to help you memorize vocabulary. (YouTube channel and business Streetwise Hebrew uses this system too on it's learning Hebrew with graffiti walking tours . Here's a news piece that explains it: https://youtu.be/sQY5RVor824