If I’d want to know how time someone spent studying something, for example medicine.

I saw in some places that I need use, something like this:

“How long have you been studying medicine for”

But, I can’t understand why I need use FOR at end.

Question

If I’d want to know how time someone spent studying something, for example medicine.

I saw in some places that I need use, something like this:

“How long have you been studying medicine for”

But, I can’t understand why I need use FOR at end.

Answer

There is no need to have "for" in that sentence.

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