Translation:It's twenty-five degrees! Why do you need a sweater?
how does Зачем тебе свитер translate into "why do you need a sweater" when there is no нужен?
нужен is implied in phrases "зачем тебе...":
Your office is just around the corner. Why do you need a car?
Твой офис за углом. Зачем тебе (нужна) машина?
I am also puzzled by this one. Doesn't "зачем тебе..." rather imply why do you HAVE a sweater"?
Well тобой is instrumental, while the Locative (also known as prepositional) is тебе (same form as dative). Not sure why, in other comments they say in this example Dative is used.
Russian usually uses the word, English usually doesn't. I'm sure plus would be accepted.
I'm assuming this is in celsius, because in farenheit this question is insane, lol.
Unless you are from the Midwest, yes, it would be insane. There, nope, we'd totally say things like that.
I got it wrong for adding Celsius after the temperature is "25 degrees Celsius!" I would say that is an accurate translation because not all English speaking countries are on the metric system.
True, it's an accurate translation, but "градусов" just means "degrees". Celsius would be "цельсия".
Зачем тебе свитер? would translate as "Why do you need a sweater?". "Why do you have a sweater would be "Почему у тебя есть свитер?"
Зачем у тебе свитер sounds a bit weird to me... It sounds like there's an aim in "having a sweater":
Чтобы я смогу дать его девушке, если бы ей нужен (What are you having a sweater for? So that I can give it to my girlfriend if she needs it)
Wait - it sounds legit...
I have never ever heard this sentence structure in English. I would say it's incorrect.