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I have rewritten the questions, adding appropriate punctuation and accent marks. These can be inserted by using the Accents drop-down box.
1. ¿Cuánto tiempo hace que estudiaste medicina?
2. ¿Cuánto tiempo hace que no estudiaste medicina?
3. ¿Cuánto tiempo hace que estudias medicina?
4. ¿Cuánto tiempo hace que no estudias medicina?
The last two questions are using the
present tense of
estudiar, conjugated in second person singular, so the inquiry is about how long something
has been happening, or has
not been happening.
Your translation of number 3 is correct.
Number 4 needs to be negated - "How long have you not been studying medicine?" or "How long haven't you been studying medicine?"
The first two questions are using the same verb and conjugation, but in the
preterit tense, so the inquiry is about how long ago something
happened,
but is no longer happening, or
didn't happen.
To answer your question, numbers 1 and 4 cannot mean the same thing since different tenses are involved.
Can you come up with the right translations of numbers 1 and 2?