for / in

English as a Second Language English Vocabulary, Grammar and Idioms
1
  1. I walk to work for/in 15 minutes.
  2. I walked to work for/in 15 minutes.
  3. I am walking to work for/in 15 minutes.
  4. I have been walking to work for/in 15 minutes.
  5. I had been walking to work for/in 15 minutes, but had not reached.
  6. I exercised for/in 15 minutes.
    Are these sentences OK with either of the prepositions?
2

No. The meaning changes with ‘for’ and ‘in’.

3

Anglophile,
Please explain each sentence with ‘for’ and ‘in’ preposition.
Thanks.

4

While for indicates the length of time you might work/exercise, ‘in’ indicates the length of time you might take to start working/exercising.